SEVENTEENTH ANNUAL MEETING. 259 



Although so extremely minute these living forms vary greatly in size, and the 

 species of average dimensions will require a magnifying power of at least 1,000 

 diameters for their successful study. 



It is difficult to form an adequate conception of an amplification of such 

 magnitude, or of the extreme minuteness of the objects that require such 

 a magnification for their study. A man magnified 1,000 times would appear 

 to be as high as Mt. Washington, and yet the average microscopic forms which 

 we can successfully investigate under a similar amplification appear no larger 

 than "the points and commas of good print." 



After examining a field with a magnifying power of 1,000 diameters, we find 

 a multitude of new forms appearing when the amplification is increased to 

 2,000 or 3,000 diameters, so that we can imagine no limit to the almost infinite 

 minuteness of the smallest forms. 



Improvements that have recently been made in the construction of objec- 

 tives for the microscope, will undoubtedly enable us to become acquainted 

 with forms that have heretofore been beyond the range of our most perfect 

 instruments. 



In order to isolate the different species, so that their life history can be 

 traced and their role or specific function may be determined, a system of cul- 

 tures under definite temperatures, and inoculation under precautions to pre- 

 vent the introduction of other forms by atmospheric contamination must be 

 resorted to. For this purpose a variety of solid and liquid media are used 

 so that each particular form may be provided with suitable materials and con- 

 ditions for its nutrition and growth. The limits of a popular lecture will not 

 allow a description of the various forms of apparatus, or the particular manipu- 

 lations required in the cultivation of these organisms. It is sufficient to say that 

 the process involves the application of the principles of natural selection. The 

 struggle for existence is carried on among the diverse forms, and the one best 

 fitted for the prescribed conditions survives and becomes the dominant form, 

 while those not as well provided with nutritive materials, and a temperature 

 suited to their vital activities, will be crowded out and perish. Pure cultures 

 of each species may thus be readily made by repeatedly inoculating a new cul- 

 ture medium of the same kind, with a small drop from the preceding culture, 

 which of course contains a large preponderance of the dominant forms it is 

 proposed to breed. 



The question may now be asked: What have these minute beings in common 

 with the higher and more familiar forms of life? They all present the char- 

 acteristics of living matter, which may be briefly described as follows: 



1. Their chemical composition is exceedingly complex, although consisting of 

 but a few elements — (some 13 out of the 64 known elements). Four of these, 

 carbon, hydrogen, oxygen and nitrogen, are of paramount importance, as 

 with water, and a few mineral constituents in minute proportions, they form 

 protoplasm, which has been called the physical basis of life. Protoplasm may, 

 in fact, be designated as an essential characteristic of living matter, as it is only 

 formed under the influence of vital activities 



2. Living matter has its origin in pre-existing living matter. Life alone 

 begets life, and each living particle involves the idea of a parent from which it 

 descended. 



3. It is constantly undergoing molecular change, and a continuous process 

 of disintegration and reconstruction is essential to all vital activities. 



4. It undergoes a cycle of changes from the germ to infancy — growth, 



