NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
CONTENTS
VOL. XVI, PART II
(June 1946)
The Editorial Committee of the Imperial Council of Agricultural Research, India, takes no
responsibility for the opinions expressed in this Journal.
Original articles
VACCINATION AGAINST RANIKHET DISEASE ...
MORPHOLOGICAL STUDIES OF THE BLOOD OF
HILL BULLS IN HEALTH AND DURING ACUTE
THEILERIASIS
DISTRIBUTION OF FAT IN Dahi ...
STUDIES ON THE METHODS OF PREPARATION
OF Ghee, I. ACIDITY IN Ghee
STUDIES ON THE METHODS OF PREPARATION
OF Ghee, II. SOURING PROCESS (WITH
FOUR TEXT-FIGURES)
STUDIES ON THE METHODS OF PREPARATION
OF Ghee, III. INDIGENOUS METHODS OF
MANUFACTURE (WITH ONE TEST-FIGURE)
STUDIES ON THE METHODS OF PREPARATION
OF Ghee, IV.' METHOD OF PREPARATION AND
PROPERTY OF BUTTER AND Ghee (WITH TWO
TEXT-FIGURES)
FLUORINE
INTOXICATION
OF
CATTLE IN
INDIA, II.
EFFECT
OF
FLUOROSIS ON
MINERAL METABOLISM
FLUORINE INTOXICATION OF CATTLE IN
INDIA, III. EFFECT OF FLUOROSIS ON THE
COMPOSITION OF BLOOD
J. R. Haddow and J. A. Idnani
B. M. Prasad ...
C. P. Anantakrishnan
and Zal
R. Kothavalla ... ...
K. S. Rangappa and B. N. Banerjee
M. R. Srinivasan and B. N. Banerjee
K. S. Rangappa, M. R. Srinivasan
and B. N. Banerjee ...
K. S. Rangappa and B. N. Banerjee
B. N. Majumdar and S. N. Ray ...
B. N. Majumdar and S. N. Ray ..
Abstract
...
...
... ... ... ... ...
Notes
... ... ... ... ... ... ...
PAGE
45
54
56
65
72
83
98
107
113
121
122
46
Vaccination against Ranikhet Disease
TABLE I
Vaccination with gel vaccine
1.
2.
3.
4.
Date
1943
December 1
do.
do.
do.
December 2
do.
December 4
do.
Type of
vaccine
Fresh vaccine ...
do.
Incubated at 37°C. ...
do.
Eluates from above ...
do.
As 1, then stored 3 days
in ice ...
do.
Dose (c. c.)
1.0
0.2
1.0
0.2
1.0
1.0
1.0
0.2
No of
fowls
3
3
3
3
6
6
3
3
Result of test
10 days later
S
S
S
1D
3D
5D
S
1D
N. B. In all experiments given in this and later Tables virus controls were used and all died without
exception.
S = Survived ; D = Died.
The period at which complete immunity is established appears to be not less than
seven days. Tests at shorter intervals gave variable results.
Small scale field experiments were carried out and the results are shown in Table II.
In the case of birds vaccinated on December 28 and January 13, the vaccine was transported
some 90 miles in two days and during this time was kept on ice ; in the other cases it was
made on the spot.
TABLE II
Vaccination with gel vaccine
Date
1943
December 28
do.
December 30
1944
January 1
January 13
January 23
do.
May 26
Dose of
vaccine (c. c.)
1.0
0.2
0.2
0.2
0.2
0.2
1.0
0.2
0.2
1.0
No. and age of fowls
21 adults
10 one-day old chickens
5 one-day old chickens
6 three-day old chickens
8 five-day old chickens
10 one-day old chickens
24 adults*
75 two-day old chickens
3 adults
40 adults
Tested on day
130
17
94
115
187
105
113
113
13
90
13
103
32—40
171
91
104
89
115
No.
8
2
2
3
3
2
3
6
4
4
4
4
10
3
6
13
3
6
Tested and result
S
S
S
S
D
D
1D
S
S
S
S
2D
S
2D
3D
2D
S
2D
* Eight fowls in contact developed no immunity,
C. P. ANANTAKRISHNAN AND ZAL R. KOTHAVALLA
57
lactic acid bacteria for the preparation of dahi. Since butterfat is the most valuable
constituent of milk, it is a matter of interest to know how the fat globules are distributed
as a result of the setting of milk for dahi making. The distribution of fat in dahi would
affect its food value as dahi is generally served out in layers when offered for sale. It
was with the idea of finding out the distribution of fat in dahi and the reasons thereof
that this study was undertaken.
EXPERIMENTAL
Since milk used for making dahi is processed in various ways, some of the common
methods were adopted in this study.
Distribution of fat in dahi from boiled milk
The milk used was secured from the farm herd of the Institute. Uniform quality was
maintained as far as possible by using milk from the same animals in all experiments
in which mixed milk was used. The milk was boiled for two minutes, cooled to 98°F.,
mixed a starter at the rate of 5 per cent. ; definite amounts (250 gm) of it were placed in
glass beakers of uniform type and provided with lids. They were kept undisturbed at the
room temperature (75°F) overnight, when the product attained the form of a coagulated
mass, even though it was only a weak gel. The top layer, amounting to exactly one fourth
of the total weight of the dahi, was removed with a nickel skimmer into a beaker. The
second layer amounting to another one-fourth of the total weight of dahi, was scooped
out into another beaker. Similarly the third and the bottom layers were removed
separately. These four parts of dahi of equal weights were dissolved in strong ammonia
(5 ml. for every 100 gm. of curd) and made up to known volume and the fat percentages
in each sample was estimated by the usual Gerber method. The results obtained were
always corrected for the dilution effected. Fat was also estimated by the Rose-Gottlieb
method for a few samples and these results were in close agreement with those obtained
with the Gerber s method. Since the latter method was more convenient, it was adopted
for all the estimations. Six trials were conducted on each lot of cow and buffalo milk and
the results obtained are presented in Table I.
TABLE I
Distribution of fat in dahi
Sample No.
1
2
3
4
5
6
1
2
3
4
5
6
Percentage distribution of fat in the different layers
Top layer
Second layer
Third layer
Bottom layer
Cow-milk
49.7
49.1
49.0
48.3
48.6
49.4
27.4
22.1
22.2
23.8
24.1
21.2
17.0
20.2
19.0
19.8
22.3
19.9
5.9
8.6
9.8
7.9
7.7
9.4
Buffalo milk
52.7
50.7
48.4
49.4
51.9
48.1
21.6
23.6
26.4
23.8
23.4
26.3
16.9
20.3
18.0
18.5
18.8
18.6
8.8
5.4
7.1
7.9
5.8
7.1
58
Distribution of Fat in Dahi
From the data it is clear that the top layer contains about 49.0 per cent of the total fat in
dahi and the second, third and bottom layers contain 23.5, 19.9, and 7.6 per cent respectively,
Distribution of fat in dahi from raw milk
Milk plasma consists of a mixture of various colloids and crystalloids. It is not expected
that these two groups of substances exert a similar influence on cream rising in dahi pre-
pared from raw and processed milk. The specific gravity of plasma is determined largely
by the mineral salts and lactose in true solution so that it is a matter of speculation
whether dahi from processed milk could show normal fat rising properties, as observed
in dahi prepared from raw milk. To ascertain this the effect of raw milk on the ascent of fat
in dahi was next studied. The same procedure as described previously was repeated using
three samples each of cow and buffalo milk. The results obtained are presented in Table II.
TABLE II
Fat distribution of dahi from raw milk
Sample No.
1
2
3
1
2
3
Percentage distribution of fat in the different layers
Top layer
Second layer
Third layer
Bottom layer
Cow milk
59.9
60.0
57.7
20.5
21.1
21.99
15.2
14.1
15.7
4.4
5.0
5.2
Buffalo milk
62.5
63.0
62.8
17.5
18.3
17.2
16.4
14.6
16.3
3.5
3.3
3.6
The dahi obtained from raw milk was of a markedly loose texture, but the dahi
from raw buffalo milk was comparatively firmer than that from raw cow milk. The body
of dahi from raw milk was not firm enough to separate it into layers easily and during
handling whey separated from the body of dahi. From the data collected, it can however
be concluded that there is more ascent of fat in dahi from raw milk as compared to that
from boiled milk. On an average the percentage of fat distribution on the top, second,
third and bottom layers were 61.1, 19.4, 15.4 and 4.2 respectively. There appears to be
no difference in the general distribution of fat in different layers of the dahi from cow
or buffalo milk.
Distribution of fat in dahi from pasteurized milk
Milk was pasteurized by maintaining it at 145°F. for 30 minutes and then by cooling
it to 98°F. It was then inoculated with a vigorous starter culture. Four samples of
buffalo milk were tried and the results obtained are presented in Table III.
TABLE III
Fat distribution in dahi from pasteurized milk
Sample No.
1
2
3
4
Percentage distribution of fat in different layers
Top layer
54.0
52.7
50.6
53.1
Second layer
22.4
22.0
22.7
22.4
Third layer
21.0
20.2
21.3
20.6
Bottom layer
2.6
5.0
5.4
3.9
C. P. ANANTAKRISHNAN AND ZAL R.
KOTHAVALLA
59
The data presented in Table III show that there is no difference in distribution of fat
in dahi prepared from boiled or pasteurized milk.
Effect of height of the column and surface area of dahi on the fat distribution
From the results of the above experiments it can be concluded that depth of the
column remaining the same, the percentage distribution of fat in different layers of dahi is
similar. However, it was of interest to study whether (a) the depth or the height of the
column of dahi has any relation to the percentage of fat distribution in dahi and (b)
the depth remaining the same, the surface area of dahi has any effect on the percentage of
fat distribution. In order to investigate these problems, boiled milk after inoculation with
a starter was placed in four tiered cylindrical glass containers of surface area 8.6, 10.8,
13.8 and 15.7 sq. cm. with a depth of 9 cm. and kept overnight Next morning, the dahi
in each container was analysed for fat distribution. The same experiments were repeated
with the same containers, but varying the height to 6 cm. and also to 3 cm. In all cases
three samples of buffalo milk were taken for the experiments. The results obtained are
presented in Tables IV, V and VI.
TABLE IV
Effect of surface area on the distribution of fat in dahi
Height of dahi 9 cm.
Sample No.
1
2
3
1
2
3
1
2
3
1
2
3
Surface area in
sq. cm.
8.6
10.8
13.8
15.7
Percentage distribution of fat in different layers
Top layer
52.9
52.6
51.9
54.2
52.4
51.7
50.4
53.9
52.9
54.7
51.9
53.2
Second layer
21.5
21.7
21.1
21.9
22.3
21.9
23.0
23.5
22.7
19.2
22.3
21.9
Third layer
18.2
16.9
18.6
18.7
19.4
18.3
20.0
17.1
18.3
18.0
19.1
20.2
Bottom layer
7.4
8.8
8.4
5.2
5.9
8.1
6.5
5.3
6.1
8.0
6.7
4.7
TABLE V
Effect of surface area on the distribution of fat in dahi
Height of dahi 6 cm.
Sample No.
1
2
3
1
2
3
1
2
3
1
2
3
Surface area in
sq. cm.
8.6
10.8
13.8
15.7
Percentage distribution of fat in different layers
Top layer
64.6
65.0
63.8
62.7
62.6
63.2
64.0
63.0
64.7
63.5
63.1
60.9
Second layer
20.2
19.0
19.3
20.4
19.4
19.3
20.5
20.0
18.7
20.0
18.8
20.0
Third layer
12.6
11.8
13.4
14.0
12.6
14.4
13.3
13.8
13.3
14.0
12.7
14.4
Bottom layer
2.5
4.2
3.4
3.0
5.3
3.2
2.2
3.2
3.3
2.4
5.3
4.7
60
Distribution of Fat in Dahi
TABLE VI
Effect of surface area on the distribution of fat in dahi
Height of dahi 3 cm.
Sample No.
1
2
3
1
2
3
1
2
8
1
2
3
Surface area in
sq. cm.
8.6
10.8
13.8
15.7
Percentage distribution of fat in different layers
Top layer
90.7
87.5
89.5
92,2
89.4
89.5
92.2
87.5
91.4
91.5
87.6
90.8
Second layer
5.5
8.1
6.8
5.6
6.3
5.4
5.4
7.6
5.8
5.6
7.6
6.0
Third layer
2.0
3.2
2.6
1.4
2.6
3.4
1.6
3.8
2.0
1.7
3.2
1.7
Bottom layer
1.8
1.2
1.2
0.7
1.6
1.7
0.8
1.0
0.7
1.1
1.6
1.4
Tables IV, V and VI clearly show that the depth of milk kept for dahi setting being
constant (say 9, 6 or 3. cm.) the surface area (ranging from 8.6 to 15.7 sq. cm.) has no
effect on the fat rising in dahi. It can, therefore, be concluded that the fat rising in dahi does
not depend upon the surface area of dahi. On the other hand there is a relation between the
percentage distribution of fat and the depth of milk kept for dahi setting. As the depth dec-
reases the percentage of fat in the top layer progressively increases irrespective of the surface
area, with the result that up to 90.0 per cent of the total fat could be recovered in the top
quarter layer. When the depth of milk kept for dahi making was 9 cm. the percentage dis-
tribution for the top layer was found to be 52.7, 21.0, 18.6, and 6.8 respectively. But when
this depth was only 6 cm. the distribution of the same was 63.4, 19.6, 13.3, and 3.5 res-
pectively. When the depth was still further reduced to 3 cm, the top layer contained 89.9,
second layer 6.3, third layer 2.5 and bottom layer 1.2 per cent of the total fat in the curds.
Thus, if two layers from the top are taken into consideration about 96.2 per cent of the
total fat could be recovered without disturbing the last two bottom layers. This means
that only the top half layer of dahi could be utilized if butter is to be made by the desi
method and the amount of material for churning could thus be reduced to half which
would ultimately mean a saving of labour and time.
Effect of added substances to milk on the fat distribution in dahi
Rahn
[1921]
found that when the viscosity of milk was increased, the rate of creaming
instead of slowing down was actually accelerated. An addition of gelatin causes a quick
cream-rise, a thicker cream layer and a much more complete separation of fat as cream, in
spite of the fact that the viscosity exceeds the maximum of normal milk (2.4). The ad¬
dition of crystalloids like sugar delays creaming whereas the addition of colloids like gum
arabic, peptone and albumin accelerates creaming. Dam and Sirks [1922] found that addi-
tion of colloids like starch, gelatin and gum tragacanth to milk gave a 15 to 25 per cent
increase in the volume of cream. Hammer [1916] added viscogen and found very deep
cream layers, often extending nearly to the bottom of the creaming cylinder. But all these
authors refer only to milk or cream and no work appears to have been done on the effect
of added substances on the ascent of fat in dahi. In the present investigation the effect of
colloids and crystalloids on the percentage of distribution of fat in dahi was investigated.
C. P. ANANTAKRISHNAN AND ZAL R.
KOTHAVALLA
61
Milk (250 ml.) was boiled in a vessel (degchi) with the required amount of various sub-
stances, cooled down to 98°F and brought to the original volume by the addition of water.
The samples of milk containing the various added substances were then inoculated and
transferred to glass containers to a known height (9 cm.). One sample of boiled, cooled
and inoculated milk was used as control. Agar agar 0.1 and 0.2 per cent, gelation 0.5 per
cent, starch 0.5 per cent and cane sugar 0.5 and 1.0 per cent were tried. The results ob-
tained are presented in Table VII.
TABLE VII
Effect of added substances on the distribution of fat in dahi
Sample No.
1
2
3
4
5
6
7
8
Details
Control
Agar 0.1 per cent
Agar 0.2 per cent
Control
Agar 0.1 per cent
Agar 0.2 per cent
Control
Agar 0.1 per cent
Agar 0.2 per cent
Control
Agar 0.1 per cent
Agar 0.2 per cent
Control
Agar 0.1 per cent
Agar 0.2 per cent
Control
Gelatin 0.5 per cent
Starch 0.5 per cent
Control
Cane sugar 0.5 per cent
Cane sugar 1.0 per cent
Control
Cane sugar 0.5 per cent
Cane sugar 1.0 per cent
Percentage distribution of fat in the different layers
Top layer
50.0
82.5
85.0
45.3
84.6
95.4
50.0
83.1
86.2
51.5
84.0
87.6
54.0
91.5
91.7
53.7
92.5
61.3
51.5
41.8
41.5
50.3
45.3
44.6
Second layer
25.0
7.0
7.0
24.9
6.6
2.3
22.9
9.2
6.9
23.2
5.3
4.5
22.4
2.8
2.8
21.2
4.0
17.7
20.6
26.6
24.7
21.2
23.4
23.9
Third layer
18.0
6.0
4.6
23.2
5.5
1.1
20.2
4.6
4.1
21.3
5.3
5.6
21.0
2.8
2.7
20.0
2.5
10.2
18.5
20.9
23.4
19.1
22.5
22.0
Bottom layer
8.9
4.6
3.5
6.6
3.3
1.1
6.8
3.1
2.8
4.0
5.3
2.2
2.6
2.8
2.7
5.0
1.0
10.2
9.3
10.6
10.4
9.4
8.8
9.5
It is very interesting to note from Table VII that the addition of agar agar or other
colloids prior to the inoculation with the starter results in a product possessing about 85
per cent of the total fat on the top quarter layer even though the depth of dahi was 9 cm.
This definitely shows that colloids accelerate the ascent of fat during the setting of dahi,
The crystalloids on the other hand depress the fat ascent in dahi. The agar agar always
62
Distribution of Pat in Dahi
gives a firmer curd and a richer looking product. This procedure of adding agar agar
is generally followed in the preparation of certain commercial products especially in
Bengal. In another experiment dahi was made in mud pots 9 in. depth holding 40 lb. of
milk with 0.1 per cent agar agar. The top quarter layer was removed and churned accord-
ing to the desi method. Six trials were conducted. Sixty eight per cent of the total fat
was recovered in the top quarter layer as butter. When the second quarter was also taken
for churning 79.6 per cent of the total fat was recovered. Thus, it is clear that, if agar agar
is added to milk before boiling the volume of curd to be churned, and consequently the
labour involved could be reduced by half without affecting the yield of butter to a consider-
able extent.
Effect of temperature on the distribution of fat in dahi
In order to verify to what extent stirring of milk before coagulation set in affected the
distribution of fat in dahi, milk was boiled and after inoculation placed in a glass container
to a depth of 9 cm. and kept at 98°F. One sample was kept at room temperature as control.
A third sample was kept at 98°F. with starter added to it at the rate of 10 per cent.
The depth of dahi was kept the same in all cases. After 12 hours the dahi was separated
into four equal layers and the fat percentage determined. Buffalo milk was used and
six trials were conducted. The results obtained are presented in Table VIII.
TABLE VIII
Effect of temperature of milk on the distribution of fat in dahi
Sample No.
1
2
3
4
5
6
Temperature
in degrees F.
79
98
79
98
79
98
77
98
79
98
79
98
Percentage distribution of fat in the different layers
Top layer
48.0
48.9
53.3
52.9
53.6
54.1
54.0
54.3
52.9
53.1
53.1
52.7
Second layer
23.4
20.6
20.4
21.9
19.7
20.0
23.4
22.9
21.3
22.7
21.6
21.9
Third layer
20.3
2.16
18.7
19.3
18.5
18.2
18.5
19.6
20.1
20.5
20.2
20.8
Bottom layer
8.3
8.8
7.6
5.9
8.2
7.7
4.0
3.2
5.7
3.7
4.1
4.6
Table VIII shows that there is no difference in the distribution of fat between the
samples kept at low and optimum temperatures for bacterial growth. It also indic
using more starter, and thereby shortening the time of coagulation, has no effect in supress¬
ing the ascent of fat in dahi.
Effect of stirring on the distribution of fat in dahi
To study the effect of stirring on the distribution of fat in dahi the following experi-
ments were conducted. Boiled buffalo milk was cooled to 98°F., inoculated with starter at
the rate of 5 per cent and placed in four containers to an exact depth of 9 cm. These con¬
tainers were kept at 98°F. One of the containers was kept as a control without disturbing.
C. P. ANANTAKRISHNAN AND ZAL R.
KOTHAVALLA
63
The second, third and the fourth containers were stirred well with a glass rod one and a
half, two and three hours respectively after inoculation. After this, the samples were
allowed to remain in the incubator undisturbed for 12 hours and were then separated into
four equal layers and analysed for fat. Six trials were conducted and the results obtained
are presented in Table IX.
The data in Table IX indicates clearly that stirring the product two or three hours after
inoculation brings about a better uniformity in the distribution of fat in different layers.
In samples stirred one and a half hours after inoculation, the fat percentage of the top
layer was generally more than those stirred two or three hours after inoculation. In all
the above samples visible coagulation was observed only 4.5 to 5.5 hours after in-
oculation. The effect of stirring four hours after inoculation on the distribution of fat
in different layers was also investigated. Three trials were conducted using boiled cow
milk and the results obtained are presented in Table X.
TABLE IX
Effect of stirring milk after inoculation on the distribution of fat in dahi
Sample No.
1
2
3
4
5
6
Hours after in¬
culation at which
stirring was done
Control
1.5
2.0
3.0
Control
1.5
2.0
3.0
Control
2.0
3.0
Control
1.5
2.0
3.0
Control
2.0
3.0
Control
1.5
2.0
3.0
Percentage distribution of fat in different layers
Top layer
47.7
42.3
32.6
32.6
48.3
40.4
34.0
34.1
47.6
36.0
29.5
47.1
42.1
33.6
31.4
53.3
36.8
34.2
52.1
42.1
34.3
30.0
Second layer
20.3
23.8
24.3
25.7
23.3
24.1
25.2
25.2
23.5
23.6
24.6
23.1
23.9
24.6
26.8
20 3
23.2
24.4
21.9
24.2
23.9
25.0
Third layer
21.6
21.6
25.0
23.7
21.2
21.4
23.2
23.2
20.5
23.6
24.6
21.5
22.3
24.6
24.4
20.3
23.1
23.1
20.4
23.0
22.6
23.8
Bottom layer
10.4
12.3
18.0
18.0
7.0
14.0
17.7
17.7
8.3
16.8
21.3
8.3
11.7
17.3
17.4
6.1
16.9
18.3
5.6
10.7
19.2
21.2
64
Distribution of Fat in Dahi
TABLE X
Effect of stirring milk on the distribution of fat in dahi
Sample No.
1
2
3
Hours after inocu-
lation at which
stirring was done
Control
4.0
Control
4.0
Control
4.0
Percentage of distribution of fat in different layers
Top layer
51.5
32.6
47.8
31.9
49.3
32.1
Second layer
20.6
23.2
20.4
23.8
24.1
23.6
Third layer
18.5
22.1
21.6
23.8
20.6
22.9
Bottom layer
9.3
22.1
10.4
20.5
6.0
21.4
Here again the percentage distribution of fat in different layers approached uniformity.
The stirring before coagulation effects an uniform distribution of fat in different layers
and the coagulated mass prevents the fat globules from moving upwards. The texture of
dahi is not very much altered by the stirring within four hours of the inoculation. The
dahi kept for sale should have an uniform composition and if this is to be insisted upon,
the best procedure would be to stir the mass of milk four hours after inoculation and then
to keep it overnight when a fairly uniform composition could be achieved.
SUMMARY
During the formation of dahi butterfat has a tendency to rise and concentrate in the
top quarter layer. This phenomenon is somewhat similar to the fat rising in milk or cream.
When the depth of milk kept for dahi making was 9 cm. as in the experiments reported
in the paper the top, second, third and bottom layers were found to contain about 49.0,
23.5, 19.9 and 7.6 per cent respectively of the total fat.
When the depth of milk kept for dahi making was the same there was no difference
between dahi from pasteurized or boiled milk, whether of cow or buffalo, as far as the percent-
age distribution of fat was concerned.
The dahi obtained from raw milk was generally loose in texture and therefore there was
more fat rising in raw milk as compared to that in boiled milk.
The depth of milk kept for dahi making remaining the same the surface area of dahi had
no effect on the fat distribution.
There was definite relationship between the depth of dahi and the upward movement of
fat. As the depth of milk kept for dahi making decreased the percentage of fat in the top
layer increased, irrespective of the surface area, with the result that even up to 90.0 per cent
of the total fat could be recovered in the top quarter layer when the depth of the column kept
for dahi setting was 3 cm.
The addition of colloids like agar agar to milk before the addition of starter appreciably
accelerated creaming in dahi, whereas crystalloids like cane sugar delay creaming.
It was found that by incorporating agar agar in milk for the indigenous method of butter
making, about 80.0 per cent of the total butter fat could be recovered from the top layer of
the curd.
A fairly uniform distribution of fat in dahi could be secured if dahi is stirred within
three to four hours after inoculation of the milk with the starter culture.
REFERENCES
Dam and Sirks (1922). Verslag. Land. Onderz. Rijks, 26, 100
Hammer (1916). Res Bull. Iowa agric. Expt 31
Rahn (1291). Forsch. Geb. Milchereiw 1, 133