199 



gave rise to a comparativeh^ mild disorder, which 

 however sufficed to secure immunity against further 

 attacks" ^" in the inoculated specimen. So far as this 

 question applies to the attenuation of the virus, it 

 bears out the observations of Dr. Clarke and myself as 

 to the effects which heat and cold have respectively on 

 the power of the bacillus for harm, and although I 

 liave not instituted any definite experiments bearing 

 on the statement that a previous attack of septic 

 enteritis grants immunity against the disease, it would 

 yet seem very probable from general observations that 

 such is the case. Moreover, without ver}^ definite 

 evidence to the contrary, one would be loth to question 

 the authority of this distinguished observer. 



But while, as we see, this acquired individual 

 immunity protects onh^ isolated individuals, it is quite 

 otherwise with racial, and therefore hereditary, 

 immunity. Again we must look to the human races 

 for examples, selecting those that as far as the facts 

 connected with them are concerned, are indubitably 

 established and accepted. The negro of the West 

 Coast is immune against yellow fever ; compared with 

 his white brother the negro of any part of Africa is 

 impervious to malaria; on the other hand the white 

 man, when exposed to these diseases, not only almost 

 immediately contracts them, but generally finds them 

 fatal to him, — at any rate, the former of the two. In 

 like manner the European, living in countries where 

 the tubercle bacillus is abundant, is so comparatively 

 immune against its resultant disease, that only about 

 one out of every ten deaths from all causes is due to it ; 

 and moreover most of the cases are very chronic in 

 their course, thus showing the amount of resistive 

 power that the inhabitant of these countries has 

 attained to with respect to this particular disease. 

 Viewed merely as an absolute fact all this may appear 



* Dr. Murray, in Green s Pathology, 9th edition, igco, page 287. 



