with the addition of salts from the earth. 

 An evolutionary query might then arise 

 as to the early conditions in the history of 

 organic life on the earth. It is certainly a 

 fertile field for the theorist. Accepting 

 the general rule that simplicity of struc- 

 ture indicates priority, what then was the 

 food supply of the primordial bacterium 

 before the advent of higher plants to sup- 

 ply requisite organic matter? We can 

 hardly believe that there was already in 

 existence sufficient ammonia-bearing 

 compounds of suitable quality to sustain 

 these lowest organisms until evolutionary 

 conditions added organisms having the 

 capacity of collecting nitrogen and car- 

 bon from purely inorganic sources. 

 These general facts, as we now see them, 

 would apparently strengthen the thought 

 that different kinds of organisms became 

 extant at the same time. 



The methods used in bacteriologic 

 study are based on a few very distinct 

 principles. Successful cultivation of bac- 

 teria depends upon a knowledge of sterili- 

 zation, preparation of culture media and 

 isolation of species. It is in fact minia.- 

 ture gardening. A rod of platinum wire 

 is the trowel and this is kept clean and 

 free from undesirable organisms by heat- 

 ing it red hot in the gas flame. With it 

 bacteria are lifted from tube or plate. The 

 culture media required are mostly beef- 

 tea and gelatine mixtures and are pre- 

 pared with extreme care as to their com- 

 position and reaction. The decomposi- 

 tion of the culture medium is prevented by 

 keeping it in test tubes or flasks plugged 

 with cotton and sterilized by boiling. By 

 means of the cotton plug the air passing 

 in and out of the tube is filtered and the 

 bacteria floating in the air are caught in 

 the cotton and cannot get into the tube. 

 It also prevents bacteria from the culture 

 getting out of the tube and spreading in- 

 fectious material. Each test tube repre- 

 sents a little greenhouse, but one that is 

 free from all life ; it is sterile when ready 

 for use. To the media or culture soils in 

 the tubes the bacteria are transplanted 

 with the platinum rod, and active growth 

 is obtained by placing the tubes in a suit- 

 able temperature. Such a growth of bac- 

 teria in a test tube can contain many 

 millions of bacteria, while the resulting- 



appearance of growth is due to the heap- 

 ing up of the individuals. To the naked 

 eye the cells are invisible, but the mass is 

 recognized in the same way that one 

 would know a field of wheat in the dis- 

 tance without being able to see each sep- 

 arate plant. Species of bacteria are sep- 

 arated by distributing a few organisms 

 throughout a fluid and then planting upon 

 solid media. The individual cells then 

 grow in place and produce colonies. 

 These are separate and distinct to the 

 eye and each contains bacteria, all of the 

 same kind. From colonies transplanta- 

 tions to tube cultures are made, and the 

 species is propagated on different media. 

 The observations from such growths, to- 

 gether with the microscopical study and 

 sometimes inoculation experiments on 

 animals are the data by which the species 

 is recognized. Microscopic methods, al- 

 though somewhat complicated have been 

 so far developed that some species of bac- 

 teria can be as promptly recognized un- 

 der the microscope as an acquaintance 

 met upon the street. 



Bacteriology is now being studied and 

 investigated as a field of research in hun- 

 dreds of laboratories, and in every uni- 

 versity in Europe and America. Bacteriol- 

 ogy has added as much to man's wealth 

 and happiness as any of the applied 

 sciences. All the methods of preservation 

 of food depend upon bacteriological 

 principles, while modern sanitary science 

 is based on the recognition of the cause 

 of infectious diseases. The presence of 

 specific bacteria in the secretions or 

 tissues of man and animals is now such a 

 certainty for many diseases that the work 

 of making bacteriologic diagnoses is in 

 itself an extensive vocation. Within the 

 next few years every city in America will 

 have a diagnosis laboratory for infectious 

 diseases. We can safely predict that the 

 trained bacteriologist will be called upon 

 to stand between each sick person or ani- 

 mal and the community to direct meas- 

 ures that will prevent infection of others 

 Hygienists are learning more every day 

 as to the exact way in which disease bac- 

 teria pass from person to person, and the 

 reasons for the occurrence of diseases 

 They have learned that the accidental and 

 unusual circumstance is least important, 



7 



