1 903 Reptile Studies 1 1 3 



munity is of two kinds — Natural or Innate Immunity, and 

 Acquired or Specific Immunity. One is the natural or 

 innate power of resistance possessed by the tissues; the 

 other is a specific acquired condition, the result of previous 

 disease or of some kind of protective inoculation. 



Every animal possesses some degree of natural immunity, 

 otherwise life would be an impossibility. The degree, how- 

 ever, varies immensely, even in closely allied species, and 

 sometimes in individuals of the same species. Thus European 

 sheep are very susceptible to anthrax, while Algerian sheep 

 are comparatively immune to this condition. Field-mice take 

 tuberculosis and glanders readily, common mice and white 

 mice not at all. It is the presence of facts such as these 

 that makes the problem one of such complexity and diffi- 

 culty, and there is much to be learnt before we can explain 

 all that is involved. It would be quite beyond the province 

 of this journal to discuss even what we do know about the 

 causes of natural resistance ; my object here is to make 

 clear the distinction between that condition and acquired or 

 specific immunity, which we know a great deal about, and 

 concerning which an enormous amount of work is being 

 done at present, the direct consequence of the brilliant prac- 

 tical results in the treatment of disease which have accrued 

 from this line of investigation. 



Acquired or specific immunity, then, is the result of 

 recovery from disease, or of some kind of protective in- 

 oculation. Small- pox, scarlet fever, measles, and many 

 conditions in animals, leave the individual safe from another 

 attack for a longer or shorter period. Note particularly 

 that each condition only protects against itself, not against 

 another distinct condition. The great difference between 

 this and the conferring of immunity by inoculation is that 

 in the first case the patient has to undergo a period of 

 reaction during which something is manufactured in the 

 body which protects against the same poison in future, 

 whilst in the case of inoculation that protective substance 

 itself can be transferred ready made, and can therefore act 

 at once. So that protective inoculation can be curative as 

 well as protective, which is, of course, the whole importance 

 of the process. This is what many have sought, and are 



vol. 11. — no. 6. h 



