ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 465 







alive for three months and fragments of heart mnscle capable of pulsat- 

 ing after three months. The term culture should only be used when 

 the fragments form fresh cells characteristic of the kind of tissue. 



Amoeboid movements of cells in explanted tissue have been frequently 

 observed. They may be seen creeping along fibrin threads. Carrel and 

 Burrows showed that the fibrin threads could be replaced by silk threads. 

 Explanted cells of heart muscle show rhythmic contractions for a long 

 time, which seems to corroborate the myogenic theory of cardiac activity. 

 The ingestion of foreign bodies by explanted cells was observed by 

 Lambert, who used Lycopodium powder with explanted spleen from an 

 embryo chick. G-iant cells were in this case seen to arise from the 

 coalescence of large mononuclear migratory cells, an important observa- 

 tion, since the origin of these giant cells has been obscure. 



Metabolic processes may also be proved in explanted tissue. The 

 formation of anti-bodies has been demonstrated, and the appearance of 

 fat globules, which may be a sign of the slow dying of the cells. 



The demonstration of growth processes is more difficult, especially 

 since a similitude of growth may be brought about by swelling, deforma- 

 tion, and migration of cells. Not even the observation of mitotic 

 figures is sufficient, for the mitosis might have begun before the ex- 

 planation. An increase in the number of mitotic figures is convincing. 

 It is the general experience that mitoses are not -particularly frequent in 

 explanted tissue. Carrel has proved growth in explanted embryonic 

 tissue by counting the cells. But many observers have been unsuccessful 

 in proving genuine growth, and are inclined to deny its reality. 



A further question arises whether the new-formed cells, if there are 

 such, are characteristic of the tissue in question. Burrows found that 

 the new-formed cells developed from embryonic heart-muscle showed 

 rhythmic contractions, but most observers record that it is the con- 

 nective tissue that grows. The new-formed cells are usually stellate, 

 spindle-shaped, or roundish ; they show amoeboid movements ; and they 

 grow radially into the nutritive medium. 



According to Hada, the new-formed cells in explanted tissue do not 

 show the specific features of the original tissue ; it is difficult to say 

 whether they are epithelial or connective ; their growth is without order. 

 Weil also says that the new-formed cells do not show the function or 

 arrangement of the mother-cells. Champy found multiplication by 

 mitosis followed by de-differentiation of elements. There is a relapse 

 into an indifferent condition. 



Schumacher's general conclusion is that there is little warrant for 

 speaking of a culture of differentiated tissues or organs after explana- 

 tion. It is important, however, that the viability of isolated cells has 

 been demonstrated, and their multiplication in some cases. The con- 

 tinued differentiation of some embryonic cells has also been securely 

 proved. 



Mitochondria in Tissue Cultures.* — Margaret R. Lewis and Warren 

 H. Lewis find that the cells of fragments of embryonic tissue from the 

 chick show finely granular cytoplasm and nucleus, almost homogeneous 



* Amer. Journ. Anat., xvii. (1915) pp. 339-401 (26 figs.). 



