238 



THE AMERICAN MONTHLY 



[December, 



these, after soaking in water for a day, 

 are dried, placed in a strong solution 

 of gum arabic, and finally treated again 

 with alcohol. Sections are then cut 

 with a microtome, and stained with a 

 mixture of equal parts of a strong solu- 

 tions of safranin and methyl green in 

 alcohol, diluted with eight parts of 

 water. The safranin stains the eggs, 

 while the methyl green goes to the 

 spermatozoa and the spermatic cells. 

 The species above mentioned, Ostrea 

 edulis, is hermaphrodite. O. Virginica 

 and O. angulata, on the other hand, 

 are unisexual. It appears, therefore, 

 that at least one species of oyster is 

 capable of self-fertilization ; yet there 

 is no reason to suppose, as might be 

 inferred, that the generative organs al- 

 ternately produce male and female ele- 

 ments, thus making provision against 

 continuous interbreeding, which is not 

 a usual course of nature, and is sup- 

 posed to lead to the deterioration, and 

 even extinction, of species. These 

 observations of Mr. Ryder are of great 

 interest, and are well worthy of repeti- 

 tion for confirmation by microscopists 

 who can obtain the oysters in a suit- 

 able condition for experiment. 



A Simple Revolving Table. — Dr. 

 Matthews described a very simple and 

 inexpensive form of revolving table 

 for microscopical use, at a recent 

 meeting of the Quekett Club. It 

 differs from all other revolving tables 

 in that it is used on top of an ordinary 

 table. It consists of two perfectly 

 fiat, wooden boards, placed face to 

 face, the upper one turning on a pivot 

 in the centre of the lower. The lower 

 board should have some rubber on 

 its under surface, or some material 

 which will cause it to remain in posi- 

 tion on a table while the upper one is 

 caused to revolve. Without further 

 description we doubt not some of our 

 readers will be tempted to make such 

 an arrangement for carrying micro- 

 scope and lamp, and others would 

 doubtless be glad to know from them 

 how well it satisfies the requirements 

 of a revolving table. 



Measurements of Blood-Corpus- 

 cles. — The author of the valuable 

 contribution treating of this subject, 

 which is published on another page, 

 has brought out some facts that are 

 well worthy of consideration. For the 

 most part they must have occurred to 

 every careful investigator in this im- 

 portant field of research. All observ- 

 ers, however, are not careful, and 

 many are even careless. It is well, 

 therefore, that the sources of error 

 should be set forth ; and we trust the 

 article will prove a serious obstacle to 

 those who, with undue assurance, 

 venture to recognize human blood. 



If, as the author states, it be found 

 that the average size of human blood- 

 corpuscles is 1J4V0 instead of ijoVo of 

 an inch, it needs no words to point 

 out how uncertain are the assump- 

 tions upon which " expert testimony " 

 has been founded — upon which hu- 

 man life has been jeopardized and 

 even sacrificed. 



Fortunately, thanks to the clear 

 heads in the legal fraternity, it seldom 

 happens that erroneous scientific tes- 

 timony carries great weight in impor- 

 tant trials ; and to this fact, rather 

 than to the credit of the expert, the 

 prisoner at the bar owes his protection 

 against undeserved punishment or 

 conviction. On the other hand, pros- 

 ecutors or defendants in suits at law 

 requiring the services of microscopists 

 would do well, if they desire justice, 

 to employ experts of reputation and 

 recognized integrity, rather than those 

 who, for a trifling fee, manufacture 

 evidence to suit either side at will. 



In passing, however, it may be rea- 

 sonably asked whether it is true, as 

 might be inferred from the author's 

 words, that the objectives and appa- 

 ratus used in the past — say thirty 

 years ago — were so imperfect that 

 trustworthy results could not be ob- 

 tained by them. We may freely grant 

 that, perhaps, the micrometers used 

 at that time were not correct. This, 

 however, affects only the absolute di- 

 mensions obtained, and does not in 

 anywise invalidate the relative sizes of 



