82 



Messrs. J. A. Gunn and R. St. A. Heathcote. 



(which both show high immunity to venom) possess antitoxic properties, 

 those properties are slightly developed, and do not accord with the degree of 

 immunity. They therefore concluded that there is no correlation between 

 the naturally refractory state which certain animals possess and the anti- 

 toxic power of their sera to the toxins to which they are insensitive. 



Camus and Grley(2) found that the serum of the hedgehog possesses no 

 antitoxic action against eel serum, though this animal withstands a dose 

 twenty times greater than the rabbit. Pettit(3) found that the relative 

 immunity of the rat to diphtheria toxin is not due to an antitoxin in the 

 rat's serum. 



It may be stated generally, as the result of these and many other 

 observations on a variety of poisons and toxins, that, though isolated cases 

 are known (4) where the serum possesses unusual antagonising powers, 

 natural immunity is not generally to any extent, and probably never 

 completely, due to the presence of antitoxins in the blood. 



It has generally been assumed, therefore, from this that natural immunity 

 is due to a specific insensitiveness of the animal cells to the action of the 

 toxin. Positive proof of this assumption has not so often been brought 

 forward. One aspect of it has been carefully examined by Camus and Gley. 

 They found that the red blood corpuscles of the hedgehog (2), as well as of 

 other animals, e.g., the toad, pigeon, and bat (5), which possess a relative 

 natural immunity to eel serum, show an increased resistance to tlie 

 haemolytic action of this toxin. Those experiments seemed to establish 

 a relationship between natural immunity and cellular resistance, so far, at 

 least, as the erythrocytes were concerned, but Camus and Gley later found 

 that the red blood corpuscles of the marmot also (6), and of the cat (7), show 

 a high resistance to the haemolytic action of eel serum, though both animals 

 are extremely sensitive to the toxic action of the serum. The relationship 

 was therefore not constant. They therefore concluded that natural immunity 

 is a complex phenomenon, and that the resistance manifested by one tissue 

 does not imply a similar resistance of the other tissues of the animal towards 

 a particular toxin. 



In regard to the natural immunity of the rat to strophanthus (8), I was 

 able to show a clear quantitative relationship between immunity and cellular 

 resistance. 



I found that the minimum lethal dose of strophanthus per kilogramme for 

 the rat is thirty times the minimum lethal dose per kilogramme for the 

 rabbit. When the excised hearts of rats and rabbits are artificially perfused 

 with solutions of strophanthus — a procedure which previously removes the 

 serum — it was found that it requires about thirty times as strong a solution 



