72 FIXATION 



of general micro-anatomy and histology, and also separately for 

 its results with each cellular constituent (cell outline, ground 

 cytoplasm, mitochondria, lipid globules, nuclear membrane, 

 nuclear sap, nucleoli, chromosomes, etc.). 



A comprehensive study of this kind has never been made, but 

 a certain amount of work has been done. More than half a century 

 ago Tellyesniczky 497-499 jj-^ Budapest studied the spermatogonia 

 and spermatocytes of the salamander in paraffin sections of testes 

 that had been fixed in various ways. Unfortunately he deliberately 

 omitted to make careful comparisons with the living cell. 'So far as 

 possible', he wrote, 'we avoid the question of Lebenstretie.^ ^^"^ 

 The Austrian cytologist Pischinger *^^ studied the effects of various 

 fixatives on the nuclei of mammalian liver, with subsequent em- 

 bedding in paraffin. His results, though interesting, w^ere marred 

 by his belief in the homogeneity of living nuclei. 



For any test of this sort, it is of great importance to choose a 

 suitable test-object. There are some organs that are reasonably 

 well fixed even by indifferent fixatives. The intestine of the newt is 

 an example. Others are susceptible to distortion in various degrees. 

 One needs an organ that is difficult to fix well, so that the defects 

 of fixatives may expose themselves clearly. It seems likely that 

 protoplasm is easily fixed when it contains a high proportion of 

 protein, and conversely; but this can only be proved when the 

 interference microscope has given more information about the 

 protein-content of cells. The distinguished cytologist, Belar,^^ 

 particularly recommended the testes of grasshoppers as test- 

 objects for fixatives. The former are only available during a limited 

 season, but crickets {Acheta domesticiis) are convenient laboratory 

 animals, ^^^ and their testes are ripe at all times of year. (See 



P- 329-)^ 



As Belar remarked, the testis of the laboratory mouse is ein sehr 



heikles Object for tests of fixatives. The kidney-cortex of the same 

 animal is equally sensitive. A test of fixatives has recently been de- 

 vised ^^ in which these two organs are the objects of study. The 

 test involves the use of only a single embedding medium and a 

 single mountant, and the results are judged only from the point of 

 view of the histologist. The test is made as thorough as these 

 limitations permit. It could easily be made wider in scope. 



The testis is cut into four parts and the kidney cortex also into 

 small pieces. After appropriate washing the fixed tissues are 

 passed through graded ethanols and toluene into paraffin wax. 



