8 INFECTION AND RESISTANCE 



removed. We have recently had the opportunity to observe this in 

 a case of septicemia caused by Streptococcus mucosus, in which blood 

 culture plates showed very numerous colonies, and in which recovery 

 followed promptly upon complete excision of the thrombosed veins. 

 It would seem to us, therefore, that bacteriemia offers a rather better 

 prognosis than was formerly supposed, at least in cases in which the 

 focus is surgically accessible. 



The same principle is illustrated in the ordinary clinical course of 

 typhoid fever in the human being. Here the disease begins as a 

 bacteriemia. Very rapidly, usually within two weeks, the bacteria 

 disappear from the blood stream and a high serum immunity is 

 established in the patient. Nevertheless, the bacteria remain actively 

 growing within definite foci in the tissues, where they are to a cer- 

 tain extent protected or inaccessible to the defensive powers so suc- 

 cessfully active in the blood stream. At any rate the patient remains 

 diseased and the bacteria can be isolated from the spleen, gall-blad- 

 der, and intestines at a stage when they are no longer present in the 

 blood stream, and during which a measurement of the bactericidal 

 and opsonic powers of the patient will reveal a serum immunity 

 much higher than normal. Just why the organisms are protected 

 from these influences in the tissues we do not know. 



On the other hand, it is nevertheless true that a certain amount 

 of actual adaptation between the bacteria and the body may take 

 place and contribute to the chronicity of an infection. This seems 

 to be shown especially by the experiments of Walker and others, 

 which are referred to in other places, in which it was found that bac- 

 teria grown on immune sera gain a certain amount of resistance 

 against the injurious properties of these substances, and evidence 

 more directly bearing upon the question is furnished by the studies 

 on the typhoid carrier state in rabbits made by Chirolanza, 8 Black- 

 stein, 9 Johnston, 10 and recently by Gay and Claypole. 11 The last- 

 named writers found that they could regularly produce the typhoid 

 carrier state in these animals if they first cultivated the typhoid 

 bacilli upon a medium containing defibrinated rabbits' blood. Even 

 in these cases, however, it is not at all improbable that the typhoid 

 bacilli establish a permanent focus from which they are discharged 

 into the blood stream. 



An infectious disease, therefore, may be interpreted as the result 

 of parasitism in which no such mutual adaptation has taken place, 

 and in which the invasion of the host by the micro-organism is 

 marked by a struggle, the local and systemic manifestations of which 

 constitute the disease. The disease is an evidence of conflict be- 



8 Chirolanza. Ztschr. f. Hyg., Vol. 62, 1909. 



9 Blackstein. Bull. Johns Hop. Hosp., 1891. 



10 Johnston. Journ. Med. Res., 27, 1912. 



11 Gay and Claypole. Arch, of Int. Med., 12, 1913. 



