SIGNS AND SYMPTOMS OF DISEASE 151 



part of little or no value in controlling the progress of these disorders, 

 and it is recognized as an axiom in the treatment of all such affections 

 that the aim of the physician should be to maintain the patient's strength 

 to enable him to resist the effects of the malady during its progress, 

 which it is admitted cannot be arrested. 



The recognition of the fact that an attack of an infectious malady 

 exhausts for a certain period the susceptibility of the system, very early 

 led to the adoption of inoculation as a means of controlling the virulence 

 of the disorder, and, further, of causing the attack at a period when it 

 might be considered to be of least importance. When the inoculation 

 was properly performed, even in a virulent disease like small-pox, the 

 resulting attack was generally very mild in its character. The extremely 

 minute quantity of the virus which was employed had a great deal to 

 do with the more benign character of the infection, and the operation 

 had further the advantage of enabling the operator to determine when 

 the disease should be produced, and selecting a period when the patient 

 was in the most favourable condition. The one insurmountable objection 

 which presents itself, both in regard to man and the lower animals, is 

 the danger of communication of the inoculated disease to susceptible 

 subjects, who are as likely to suffer from a severe or fatal attack as if 

 they had taken the affection from the most virulent case. The dis- 

 covery of certain microbes which were proved to be the cause of disease, 

 and the results of artificial cultivation in modifying this virulence, turned 

 the attention of pathologists to the subject of protective inoculation by 

 means of the ameliorated virus, which was found to produce an extremely 

 mild form of the disease and to confer immunity with a very slight 

 amount of risk. This method of protection has been tried with a certain 

 amount of success in anthrax, and in the disease which is known as 

 Blackleg in young cattle. In this country the system was not at first 

 favourably received; accidents occurred among inoculated animals which 

 led to losses as great as would in ordinary seasons occur in the unprotected. 

 Improved methods of preparation of the virus, and simpler means of 

 inoculation, have since been attended with a large measure of success. 



For a long period there was only one infectious disease — glanders — 

 to which the horse was believed to be subject, and in regard to this 

 affection its infectious origin was frequently disputed. Of late years 

 the progress of the science of bacteriology has led to the addition of a 

 number of diseases which are classed as infectious, the term being now 

 understood to include disorders the virus of which may, according to some 

 authorities, be generated in the organism instead of being introduced from 

 the outside. This view, however, of auto -infection is not capable of 



