Guilliermond - Atk inson —4— Cytoplasm 



brought out by fixation and staining, their actual presence must 

 be checked by observation of living material in such cells as lend 

 themselves to it. This observation of living material permits a 

 proper appreciation of the value of the above methods. As the 

 very handling of living material runs the risk of producing altera- 

 tions, every precaution to avoid them must always be taken. 

 Fungi may be used which can be observed in their own environ- 

 ment, or organs studied which are sufficiently transparent to permit 

 their cells to be examined without any manipulation. Petri dishes 

 of a special type (used at the International Bureau for the Culture 

 of Fungi at Baarn) can be used if necessary. In the bottom of these 

 is an opening of 3 cm. which can be covered with a slide sealed 

 with asphalt cement (Fig. 88). In this way, seeds can be grown 

 aseptically and their roots during development can be observed with 

 an oil-immersion lens by turning the dish under the microscope. 

 Vital dyes must be used to enable us to follow such elements as the 

 vacuoles which are not well preserved by any other means. More- 

 over, each element whose presence has been recognized by fixation 

 and staining must be described by means of a systematic study of its 

 behavior with most fixatives and stains ; this study must be based 

 upon histochemical reactions of the element in question. This 

 method, called histochemical analysis, permits us to characterize 

 the element, to distinguish it from others, and to inform ourselves 

 as to its chemical nature. It permits us, besides, to distinguish 

 some elements which are revealed only by certain methods of fixa- 

 tion and staining. Histochemical analysis must be followed by an 

 histophysical analysis, i.e., analysis of the physical state of the 

 element, its viscosity, colloidal state, and so forth, an analysis in 

 which will be employed the micromanipulator, the ultramicroscope, 

 the polarizing microscope, the centrifuge, the plasmolytic method 

 and, if need be, motion-picture photography. This histophysical 

 analysis will supplement the description obtained by histochemical 

 analysis. Then, too, the development of the element throughout 

 the entire life of the cell must be followed in order to know whether 

 it constitutes a permanent element or is only transitory, and in 

 order to obtain an idea as to its significance by observing its be- 

 havior. Finally, it will be useful to supplement this method called 

 the analysis of the cell, which comprises the various operations just 

 enumerated and which has, itself, all the value of an experimental 

 method, by a further series of experiments designed to clarify the 

 role of the element studied. Among these experiments are vivisec- 

 tion, depriving a cell of an individual element by means of the 

 micromanipulator, and a study of nutritional influences on the be- 

 havior of the element under consideration. This is the cyto- 

 physiological method which we will turn to only occasionally here, 

 our aim being chiefly the morphological study of the cytoplasm. 

 The procedure specified is the only one by which precise facts may 

 be obtained on the morphological constituents of the cj^oplasm : the 

 plastids, chondriosomes and vacuoles. 



