64 



PROTOPLASM 



(Hevea, Fig. 89; Euphorbia; milkweed; etc.), contain the chief 

 hydrocarbon constituent of rubber. They are about the size 

 of the human red blood corpuscle. To tear them apart with 

 delicate needles gives some idea of their physical structure. 



Microinjection is one of the most promising fields of investiga- 

 tion in micrurgy. Its possibilities have only just been entered 

 upon. The effects of salts and dyes are different when injected 

 into protoplasm from what they are when the cell is bathed 

 in them. Microinjection has shown what these differences are. 



A B 



Fig. 51. — Root hairs of Limnobium with oil globules injected. At the upper 

 left in A (just over what appears to be a C) is seen the coagulum which has healed 

 the wound where the micropipette entered. The glass-like strands of protoplasm 

 (best seen in B) are streaming. {From T. Kerr.) 



"Indicator" dyes have been injected into protoplasm, and by 

 color changes the acidity determined. Needham of England 

 has performed such experiments and ascertained not only the 

 acidity but the oxidation-reduction potential of a cell. Janet 

 Plowe injected into cells dyes which do not penetrate when the 

 cell is immersed in them. It was her problem to ascertain if 

 the inability of a dye to enter a cell is due to properties of the 

 protoplasm as a whole or only to peculiar properties of the 

 surface layer. She found the latter to be the case, for the dye 

 diffuses freely in the protoplasm when injected directly into it. 

 Kerr has injected a variety of substances into root hairs of the 

 aquatic plant Limnobium. If oil droplets are injected (Fig. 51^), 

 they may be seen to travel down to the end of the cell (Fig. 515), 

 carried by the streaming of the protoplasm. 

 Many are the possibilities of micrurgy. 



