32 JOURNAL OF THE TRINIDAD 



Perfectly still air becomes pure by subsidence of these particles. 

 Bacteriological examination of air over the surface of the liquid 

 in main sewers has shown an absence of bacteria. 



All water except from great depths contains bacteria. Rain 

 water becomes contaminated from the dust which it carries down, 

 while surface water is infected from the ground through which it 

 soaks. The risk of contamination of well water and river water 

 by bacteria derived from sewage is obvious. Even sea-water is 

 not free. Dr. Bassenge of the Stosch shewed me cultivations 

 which he had made from water taken at various depths in the 

 Atlantic Ocean. 



From the above considerations it is evident that the bodies 

 of man and the lower animals are always exposed to the danger 

 of infection, and that many bacteria enter every day in food or 

 water, or attached to dust are swallowed, inhaled, or brought in 

 c intact with open wounds or sores on the surface of the body. 

 The aim of preventive medicine therefore should be not only to 

 destroy bacteria whenever possible, but also by attention to the 

 ordinary rules of health, to diminish the receptivity of the in- 

 dividual. For we cannot but believe that bacteria will continue 

 to exist in spite of all our efforts to exterminate them. 



I propose now very briefly to examine the various groups 

 and genera set forth in the classification of Zopf. I have for 

 the most vart followed Crookshank's descriptions. 



Group I. — Coccacece. 



This possesses only cocci and thread-forms resulting from the 

 juxtaposition of cocci. Fission may occur in one or more direc- 

 tions. Five genera are included in this group : — 



1. — Streptococcus. — These are known as chain-cocci, because 

 the individuals always or occasionally remain united together to 

 form chains. Division is in one direction only. 



Numerous species of streptococcus are desci'ibed, many of 

 which are associated with disease in man or animals, though to 

 what extent this relation is pathogenic has yet to be determined. 

 In this family occur the many forms of streptococcus pyogenes so 

 frequently found in the pus of abscesses. Many of them are 

 readily recognizable by the naked eye from the resemblance of 

 the colonies which grow in glycerine agar- to drops or streaks of 

 o ; l paint of various colours. Other species have been described 

 in connection with erysipelas, diphtheria, puerperal fever, endo- 

 carditis and several other human diseases, and also in many dis- 

 eases of the lower animals such as swine erysipelas, cattle -plague, 

 foot and mouth disease, disease of grey parrots, and the"flacherie," 

 of silk worms 



