76 CHAPTER V. 



LAVDOWSKY, last edition ; or the picroformol of BOUIN 

 (Phenomeiiex cytologiqut's anormaux </a?i.s V hittogenese , etc., 

 Nancy, 1897) (30 parts picric acid, sol. sat., 10 parts formol, 

 2 parts acetic acid), or the similar one of GKAF (Jonrii. Roy. 

 Mic. 8oc. t 1898, p. 492), the mixture of ORTH (10 parts 

 formol to 100 of solution of Muller [it must be freshly pre- 

 pared, as it will only keep a few days], Berlin, klin. 

 Wocheitschr., 1896, No. 13; Zeit. f. iciss. Mik., xiii, 3, p. 

 316), and the mixtures quoted under " Neurological Method* " 

 in Part II. 



It should be noted by those who desire to experiment 

 with such mixtures, that formaldehyde is a powerful reducing 

 agent, and therefore incompatible with such reagents as 

 chromic acid or osmic acid and the like, which it very 

 rapidly decomposes. 



To sum up, I feel convinced that neither strong nor weak 

 should formaldehyde be employed pure for fixing ; and that 

 it has not been shown to be of any real utility in fixing 

 mixtures, so long as faithful histological fixation is aimed at. 

 But, of course, that does not prejudge the question as to 

 whether it may not render services in cases in which faithful 

 histological fixation is only a secondary point, as in many 

 pathological researches ; nor does it imply that it may not 

 be useful for the purpose of hardening sensu stricto tissues 

 that have previously been duly fixed by some other agent. 



Considered as a hardening agent sensu strict o the most 

 important use of formaldehyde is for hardening nervous 

 tissue, for which it is now much used, perhaps with better 

 justification than for most other purposes. For this see 

 Part II. 



HERMANN (loc. cit., supra) found that such a large organ as 

 a calf's heart was entirely hardened by a 0*5 to 1 per cent, 

 in twelve to twenty-four hours. Entire eye* are so hardened 

 in the I per cent, solution in twenty-four hours that they 

 may be cut in two with a sharp knife, like an apple. Her- 

 mann found this disadvantage, that tissues hardened in 

 formaldehyde solution suffer when they are put into alcohol 

 for the purpose of dehydration. The paper in question con- 

 tains interesting observations on the property formaldehyde 

 has of preserving the natural colours and transparent and 

 lifelike aspect of tissues. 



