INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 943 



Chloride of Cadmium as a Fluid for Homogeneous Immersion.* 

 — Colonel Woodward expresses his approval of one of the new immer- 

 sion fluids proposed this year by Professor Abbe,t viz. the chloride 

 of cadmium dissolved in glycerinej^and sends photographs of Ainplii- 

 pleura pelludda taken with the Zeiss yV and Tolles' amplifier, both 

 with cedar oil and with the cadmium solution. The last picture, as he 

 points out, resembles that taken on the same day with the cedar oil 

 almost as closely as if the two were prints from the same negative. 

 The cadmium solution is not only convenient for use with objectives of 

 considerable focal length (as the L of Zeiss, for example), but is 

 especially desirable for photography, as it cannot attack the balsam 

 cement of the front lens of the objective. This he finds the oil of 

 cedar may do. Slowly as it attacks solid balsam when cold, it appears 

 to act more energetically when the temperature is somewhat raised, as 

 happens during micro-photography. In the case of the Zeiss ^ 

 belonging to the Army Medical Museum, the oil of cedar has already 

 in this way penetrated to the space behind the front lens of the 

 objective, which he has in consequence been obliged to return to the 

 maker for repairs. The substitution of the new fluid ajipears therefore 

 to have advantages for photogra2)hic purposes which are well worthy 

 of consideration. 



Scientific Value of Microscopic Preparations.^— Dr. Pelletan, 

 of Paris, complains of the small scientific value of the majority of 

 microscopic objects prepared for sale, though they are often very 

 beautiful in appearance ; the preparations of diatoms being alone, for 

 the most part, satisfactory, often excellent, and sometimes marvellous. 

 Certain preparations of cryptogamic botany are also, he considers, of 

 value, and dissections, &c., of vegetable anatomy, thin cuttings of 

 dense substances, animal, vegetable, and mineral, and particularly 

 sections of wood, but of all other classes it is only by chance one 

 meets with an interesting slide. 



Many of the ordinary preparations, however, if not satisfactory to 

 savants, interest amateurs, and they teach many things that otherwise 

 would not have been Imown. "They are also useful in England, where 

 they are sold in large numbers, because in that country the Micro- 

 scope is more used for amusement and as an object of luxury than for 

 working purposes. These slides, that for us have little interest, are 

 therefore in this point of view of real utility. They give to ordinary 

 people the taste for natural objects, and they furnish a thousand little 

 instructions acquired without labour, and are also amusing. We must 

 not, therefore, too much despise them. 



" Histological preparations, whether normal or pathological, are 

 those of least value. Preparers, with very few exceptions, have not 

 sufficient knowledge of histology or of the necessary technical methods, 

 or even the will to adopt them, because they are tedious and delicate, 

 and, moreover, it is feared that the increased cost of the preparations 

 would frighten those who might wish to acquire them. There is no 

 foundation for this last reason, judging from the daily demands for 



* See post, p. 988. t See ante, p. 346. 



X 'Journ. de Micr.,' iii. (1879) p. 139. Translated in full ia 'Science-Gossip,' 

 1879, No. 179, p. 250. 



