60 



PROTOPLASM 



great amount of dissection with apparent indifference. The 

 Plasmodium of a slime mold may be badly torn, and the stream- 

 ing of the protoplasm stopped, only to be resumed within a 

 minute or less, around the wound. 



Micrurgy has had to do primarily with the structure of cells 

 and the physical properties of protoplasm, such as viscosity, 

 elasticity, miscibility, and the nature of the surface membrane. 

 These properties will be discussed in separate chapters. Here 



Fig. 47. — Stages in the dissection of a blood cell {A, B, C). In B the hemo- 

 globin has escaped from the upper (pale) half of the cell (the nucleus is in the 

 center), while it is still within the lower half of the corpuscle which has been 

 stretched but little; D, a needle entering a living plant cell. 



we can, for the moment, select any one of them and make it our 

 task to solve it by micromanipulative methods. For example, 

 has the red blood cell or the nucleus of Amoeba a morphological 

 membrane? This question has been frequently asked. As 

 material of blood cells we can best use the corpuscle of the 

 amphibian Amphiuma, for they are very large. Two micro- 

 dissection needles are brought up into the corpuscle (Fig. 47 A) 

 in such a way as to avoid the nucleus. The needles are then 

 separated, and the cell first stretched (Fig. 475) and then torn. 

 It tears not like a mass of jelly but like a sac. The hemoglobin 

 first escapes through the membrane where stretched and damaged 

 most (Fig. 475, upper half), then through the entire membrane 

 (Fig. 47C). Finally, when the membrane is actually torn and 

 opened, the nucleus escapes. An empty sac is left behind. 



