DISEASES OP THE BLOOD. 157 



impetiginodes, is really equine variola^ and its virus intro- 

 duced into tlie system of the ox originates variola vaccinia. 

 These diseases of the two species of animal were, therefore, 

 by him considered identical. This communication of virus 

 may be direct or indirectly through attendants. Human 

 variolous matter, when introduced into the system of the cow 

 is stated to cause a smalljpGx eruption, while vaccine intro- 

 duced into the human system does not produce smallpox, only 

 vaccinia. From the eruptions in the latter case may be col- 

 lected lymph, which, when preserved in capillary tubes or 

 on ivory points, is available for other vaccinations. It 

 always produces the milder disease, and always proves 

 effective against smallpox if the lymph be good and the 

 inoculation successful. Thus, much lymph derived by 

 linear descent from that which originally came from the 

 cow is in circulation. Two important questions arise in 

 connection with it : — 



1. Has it degenerated by successive passages through 

 the systems of numerous human beings, so as to prove 

 less effectual in securing immunity now than formerly, 

 and, if so, will it not be better to renew the stock ? 

 Certainly, lymph just taken from the cow produces more 

 marked effects than humanised lymph, but this is not always 

 a benefit. The lymph of the present day ordinarily acts 

 with quite sufficient potency and seems to be very effectual. 



2. Has it become admixed with human specific poisons — 

 scrofula, syphilis, and the like, which would not be 

 present in animal lymph. There is much feasability in 

 this argument in favour of animal vaccination. Un- 

 doubtedly there is much vitiated lymph in circulation. 

 Some lymph '^ stocks '' are very pure, in consequence of 

 great care in selection of lymph for preservation. The 

 production of fresh supplies of lymph from the cow is, 

 therefore, by all means to be encouraged, but good old 

 lymph is not to be rejected, as it is decidedly better for 

 weakly subjects. Vaccination and other inoculations are 

 performed by removal of the epidermis, and insertion of 

 the virulent fluid on the exposed surface of the cutis. 

 Blood should not be drawn, for this would tend to wash 



