amoeba white cells whose work it is to remove foreign materials from his blood the white cells cannot dispose of them by the under stimulus of the germs tiny particles called at him bodies are being produced and at first the germs increase faster than the other bodies if this continues the patient gets steadily worse and may even die usually however as in this case the bodies are produced faster than they are it up and it becomes only a matter of time until the germs are all disposed of and the patient recover and so this child has what we call active and because he has developed his body is acquired this act of immunity by actually having the disease fortunately there is a safer way to get immunity through vaccinate in vaccination a substance called a vaccine is introduced into the body the body responds by developing and a body is just as in the case of an actual infectious disease unlike the disease however of that scene does not endanger life let's study three types of vaccines large quantities of vaccine are produced by infecting healthy calves like this one with live cowpox myra's the virus multiplies rapidly and by the fifth day crusts have formed on the skin where ever the calf was infected these crusts are collected they contain the live germs which will serve as vaccine for human beings from this mixture individual doses of the vaccine are prepared the vaccine may be supplied in a capillary tube like this and apply directly to the skin from the t in this disease the other bodies dispose of the germs probably without the help of white cells the child to say from smallpox for several years another type of virus vaccine is used to protect against poliomyelitis here a second type of vaccine is being made pneumococcal side the germs that cause lobar pneumonia are being used for this vaccine dead germs are needed because there is no we can form of pneumococcal side as there is a smallpox virus the live germs are killed with chemicals or with heat as in this case now let's see how this vaccine made from dead germs works when injected into a live animal the effect would be the same in a human in the rabbit's bloodstream the dead germs shown as pairs of ovals stimulate the formation of added bodies as additional injections are given more and more added bodies form and combine with the germs which are then removed by the white cells this rabbit has now developed active immunity to pneumococcus infections now let's take a sample of this after standing a few hours the blood drops and the serum containing the added body is separate from a few drops of the serum or added to a culture of pneumococcal sigh the alley bodies come in contact with the germs clumps of germs that ivy bodies settled to the bottom this is called a gluten nation now let's see how the same serum acts in the case of a rabbit already stricken with a pneumococcus infection first the serum is injected into the rabbit's bloodstream so when the added bodies in the acquired serum begin helping the white cells dispose of the germs in about two days the rabbit recovers he has passive immunity passive because he did not develop his own added bodies but acquired them from the serum of another rabbit a third type of vaccine involved the use of poison given off by certain kinds of bacteria in depth area illnesses produced by this poison or talks him the his first separated from the bacteria next formaldehyde is added to the toxin formaldehyde counteracts the poison but does not destroy its ability to stimulate the production  the talk side is packaged ready for use it is safe even for tiny babies and doctors usually recommend vaccinating children against diphtheria before they are one year old child is given this injection the talk so i'd stimulates the production of antibodies be that a bodies are effective against diptheria toxin after an interval of time a second dose of talk so i should be in this is called a booster dose if this is done the child will usually be immune to the period throughout childhood and need not fear the disease even though it is right next door techniques for controlling infectious diseases have been developed primarily through the work of scientists whose painstaking search for new knowledge and improved methods is neverending animal to play an important role in the experimental development and in the production of vaccines vaccines against the diseases we have studied and against many others including typhoid cholera plague commercial laboratories make possible the large scale production of vaccines that meet required standards finally the campaign against infectious disease can succeed only a public cooperate