INFECTION AND IMMUNITY. 169 



of a second germ streptococcus, for example, with the anthrax bacillus 

 may render a virulent organism comparatively innocuous. But the con- 

 ditions of the experiments are in either case so complex that the full sig- 

 nificance of many curious phenomena is not yet apparent. 



Congenital Infection. Infection of the foatus through such lesions of 

 the placenta as permit of the passage of pathogenic micro-organisms from 

 the blood of the mother to that of the child is of occasional, but not fre- 

 quent, occurrence. While the barriers against such transmissions are, 

 under normal conditions, effective, disturbance in the placental circula- 

 tion, lesions of the vessel walls or of the tissues and covering of the 

 choriouic villi favor it. But infection may occur without demonstrable 

 evidence of such lesions. Thus f ostal infection is known to have occurred 

 in various phases of suppurative inflammation, in tuberculosis, typhoid 

 fever, anthrax, syphilis, the exanthematous fevers, etc. There is con- 

 siderable evidence that rarely the tubercle bacillus may be transmitted 

 from mother to offspring, and remaining for a time inactive may later 

 induce the characteristic lesions. 1 



Terminal Infection. The victims of chronic disease of the heart, blood- 

 vessels, kidneys, liver, etc., are particularly susceptible to the incursions 

 of pathogenic micro-organisms and to infectious diseases of one kind or 

 another. Such persons, with or without definite lesions, are in fact liable 

 finally to succumb to the complicating disease. The phrase "terminal 

 infection " has been applied by Osier and others to this concurrence of 

 diseases of such different nature, in which the chance infection of a vul- 

 nerable organism is so apt to prove fatal. 2 



Great care is, however, necessary in determining the significance of 

 the various forms of bacteria which may be present in the body after 

 death. Not only may bacteria develop to a considerable extent in the 

 body during the hours which precede death when the natural protective 

 agencies are halting or abeyant, but this may occur without such a re- 

 action on the part of the body cells as is necessary to constitute an actual 

 infection. Furthermore, multiplication and distribution of bacteria in 

 the body after death is of frequent occurrence and must in every case be 

 taken account of in weighing the evidence for terminal infection. 3 



COM MUNIC ABILITY OF INFECTIOUS DISEASES. 



It is important in practical dealings with the infectious diseases to 

 consider them in the light of the relative liability of transmission of the 

 actually known or assumed micro-organisms from diseased to healthy 

 individuals. 



In the first place, it should be borne in mind that the lower animals 



1 For bibliography and summary of foetal infection see Lubarsch, "Ergebnisse der 

 allg. Aetiologie der Menschen- und Thierkrankheiten," Jahrg. i., p. 427, 1895; also 

 Fixchl, Grancher, Comby, and Marfan's "Traite des Maladies de 1'Enfance," t. i., p. 

 454, bibliography. 



2 For a study of this class of cases see Flexncr, Transactions Association American 

 Physicians, vol. xi., p. 229, 1896. 



3 Consult Achard and Phitlpin, Arch, de Med. experimentale, vol. vii., p. 25, 1895. 



