172 THE AMERICAN MONTHLY [September, 
the April number of the Deztal Cosmos.’ The writer also made examina- 
tion of specimens said to exhibit the reticulum, but could not make out the 
reticulum nor, in fact, anything resembling one. It is both easier and pleas- 
anter to agree with one’s friends and co-workers than to disagree, and it 
seems an ungracious task to criticise those who have shown you kindness 
and courtesy, but the cause of truth cannot allow these strange views, so 
dogmatically asserted, to remain longer unchallenged. 
The crystallography of butter and other fats.—II. 
By Dr. THOMAS TAYLOR, 
U. S. AGRICULTURAL DEPARTMENT, WASHINGTON, D. C. 
EXPLANATION OF PLATE III. 
Figs. 1, 2, 3, 6,8, 9,12, and 14. Primary crystals of normal butter. x 80 
to 110. 
Figs. 4, 7, and 10. Primary crystals showing ‘ secondaries’ forming. 
Figs. 13 and 15. Secondary crystals of butter. 80 to 140. 
Figs. 5 and ri. Tertiary crystals of butter. > 80 to 140. 
MICROSCOPICAL TECHNIQUE. 
Making lantern slides. 
By C. M. VORCE. 
CLEVELAND, OHIO. 
In the May, 1885, number of the Yournzal (vol. vi, p. 84), I published 
a carbon process for making lantern slides, which, by later experiments, I 
have learned is liable to mislead and which I wish now to amend, since the 
many letters and inquiries I have received on the subject is evidence that con- 
siderable interest in the subject exists. 
It happened, entirely by chance. that in testing the process published as 
above I used negatives made from slides of injected tissues,.in which nega- 
tives the vessels filled with carmine had left the plate almost entirely unim- 
pressed, while the transparent tissue substance had given a dense field. Sil- 
ver prints from such negatives show but little else “than the injected vessels 
standing out boldly on an almost white ground. The result in making lan- 
tern slides from such negatives is, that the sensitive film of gelatin is str ‘ongly 
impressed with the image of the injected vessels and remains soluble in all 
other parts, and a strong transparency of the vessels is produced. 
With negatives showing tints and half-tones, however, the above process 
will not succeed, for the reason that the whole field will print to some extent 
and thus prevent washing out the underlying soluble gelatin. It becomes 
necessary, therefore, with such negatives, and is the preferable plan in all 
cases, to modify the process by what is called the single transfer in carbon 
printing. For this purpose the gelatin film is prepared upon paper instead 
of glass and is sensitized after drying. The proportions of the ingredients 
admit of wide variation, as also does the strength of the bichromate sensitiz- 
ing bath; but the best results in any case are obtained bya certain relation 
between the composition of the film, the strength of the bath, the drying of 
the film, the exposure, and the development, just as is the case in silver print- 
ing and photographic processes generally. 
For lantern slides great density is not desirable, but clear lights are impera- 
