50 BIOLOGY 



the most minute living things (certain bacteria) seem to possess 

 a body in which there is no definite nucleus, but in which the 

 chromatin matter is more or less scattered without being aggre- 

 gated into a nuclear mass, and this has led to the suggestion 

 that perhaps the simplest life unit may be an excessively minute 

 granule of chromatin with delicate fibrils extending from it, and 

 that a cell is a combination of many of these minute elements. 

 Other facts disclosed by the minute study of many animal cells, 

 with very high magnifying powers and under special conditions, 

 have pointed to a similar conclusion. As a result there has been 

 advanced recently a theory that the cell is far from the simplest 

 unit of life, and that it can be analyzed into a great number of 

 minute elements called "chromidial units," each made of a 

 granule of chromatin with fibers of linin radiating from it. 

 According to this theory the whole cell is made of a network 

 of linin fibers with granules at the nodes, each granule thus 

 representing a life unit far simpler than a cell. This has been 

 called the "protomitomic network." This protomitomic theory 

 is as yet only a matter of speculation, and its chief interest 

 to-day is in the fact that it suggests that the cell may be far 

 from the simplest unit manifesting life. Whether this new 

 suggestion be established or not, it seems certain that the 

 manifestation of life requires the presence of three elements: 

 (1) chromatin material, (2) delicate fibrils radiating from it, and 

 (3) of a liquid material in which the other parts are embedded. 

 As yet we know of nothing simpler than a combination of these 

 three that is able to manifest all the properties of life. 



LABORATORY WORK ON CELLS 



A satisfactory study of cells requires familiarity with the microscope and 

 considerable skill in microscopic methods. Little can be wisely undertaken 

 by elementary students, beyond the examination of prepared specimens, 

 properly stained, which should be furnished by the instructor. Drawings 

 should be made by the student in all cases. The cellular structure of animal 

 tissues may be studied in the following preparations: 



Blood. A small drop of frog's blood in a little normal solution (.9% 



