150 Tra?isactions. — Miscellaneous. 



The secret of the reaction has been followed by hundreds 

 of scientists for many years. Briefly, we know the following 

 facts : In the blood of man or animal which has acquired 

 immunity we can demonstrate the existence of either one of 

 two powers ; sometimes they both exist together. These 

 are — (1) Bactericidal power — that is, the blood can destroy the 

 living germ in a way normal blood does not ; (2) an anti- 

 toxic power — that is, a power of neutralising the separated 

 toxin or poison of the germ. These powers are shown against 

 the special germ of the disease we are dealing with, but not 

 against others, unless they are very closely allied. 



The bactericidal power is found in the blood of a typhoid 

 patient, and it is also shown to exist in even stronger amount 

 in the spleen and glands, where it probably originates. The 

 blood of cholera and plague patients also possesses this power, 

 and in animals it can be developed by inoculating them with 

 these diseases. Its existence can be readily demonstrated, 

 and this is now done daily in the laboratory as means of 

 diagnosing the disease. A living culture of typhoid germs 

 examined under the microscope shows a wonderful activity. 

 If we mix a minute quantity of blood from a typhoid patient, 

 diluted with, say, fifty times its bulk of water, with a little of 

 the living culture of the typhoid, and examine again under the 

 microscope, we soon see, instead of the germs moving actively 

 as they normally do, a slowness of their movements, till finally 

 they become motionless, and go into clumps. If this mixture 

 is placed in the living body of an animal we find that not only 

 do the germs get motionless, but they are in perhaps half an 

 hour destroyed altogether. Had the blood been that of an 

 ordinary person the bacteria would go on living, and if the 

 mixture were placed in the body of the animal the animal 

 would soon develope symptoms of poisoning. Here we have 

 the elements of immunisation against typhoid. The blood of 

 the person who has suffered from the disease possesses a 

 power of protecting him against further inroads, and also can 

 be used to protect other animals. This has not yet been per- 

 fected in practice, but we know that in Africa the troops 

 inoculated in this way showed for a time at least a partial 

 immunity from the disease. 



The anti-toxic power — that is, the existence of an antidote 

 to the poisons which the germs secrete during their growth — 

 is well shown in the case of diphtheria. The anti-toxin acts 

 not on the germ, but on its products. This anti-toxin can be 

 manufactured by inoculating living animals (the horse is 

 generally used) with small doses of the toxins which form in 

 artificial cultures of living germs. If we give too big a close 

 the animal will die, but if we begin with a small dose and 

 gradually increase it the animal acquires an immunity until 





