Immunological Studies in Tuberculosis
Authors: Petroff S. A. , Steenken, Wm. 
Published: December 2022

Summary
In the preceding pages, an attempt has been made to compare the resistance established in guinea pigs vaccinated intraperitoneally, subcutaneously and perorally, with living BCG, heat-killed H37 and living R1 organisms. In previously published studies, we have pointed out, that guinea pigs treated with heat-killed organisms, develop skin hypersensitiveness and also a considerable degree of protection to living virulent tubercle bacilli. Therefore, it should be of great importance that this method of vaccination was carried along with that advocated by Calmette for comparison.
Four experiments are described covering a period of almost two years. The number of guinea pigs dying from intercurrent diseases, were very few when compared with the deaths in previous years. Most of them died from tuberculosis, and the few survivors were killed to terminate the experiment.
These studies are divided into the following experiments: (a) Intraperitoneal vaccination with living BCG cultures; (b) subcutaneous vaccination with living BCG cultures; (c) intraperitoneal injection with heat-killed H37 cultures, and (d) subcutaneous inoculation with living R1 cultures. The same number of animals were used in each group. After a suitable time following the sensitization, the vaccinated and control animals were inoculated subcutaneously with 500 living tubercle bacilli of human origin.
Table 1 shows that the resistance established by BCG vaccination was in no way greater than that established in animals, which had been vaccinated with heat-killed tubercle bacilli. However, it may be noted that the animals vaccinated with living R1, apparently showed a slightly greater protection than either of the others.
In the second experiment, vaccination with the R1 was omitted, and the infecting dose was smaller. Decreasing the dose was done for the reason that the H37 strain is one of considerable virulence. We have, repeatedly, been able to produce progressive tuberculosis with as small a number as ten bacilli. In this experiment, there was evidence of protection from BCG, but again we must point out that the degree of protection was not greater than that produced when the heat-killed bacilli were used.
The third experiment was similar to the second one, so far as sensitization and virulent infection was concerned. However, the portal of entry was the testis, and only 50 organisms inoculated. Again, the animals vaccinated intraperitoneally with living BCG cultures manifested some degree of protection, and the disease was not as extensive as in the controls.
The second group (vaccinated with heat-killed H37) showed a little more resistance than the preceding one. Five animals of this group were apparently free from tuberculosis. We can only speculate whether the animals vaccinated with living BCG may have developed a progressive tuberculosis from the vaccinating organisms or from the test infecting dose.
The fourth experiment is a study of vaccination by feeding, as advocated by Calmette and his followers. (Young animals of approximately the same age and weight were selected, and separated into three groups.) The feeding was done with capillary pipettes. None of the animals fed either with BCG or heat-killed organisms, developed any hypersensitiveness to tuberculin up to the fourth week, or 49th day from the beginning of the experiment. They were infected by the inhalation method, and in table 4, we can see that guinea pigs vaccinated by feeding developed almost as much disease as the controls.