LUBRICATING TISSUES 387 



aim is to fix in some fluid that will harden the elements as little as 

 possible and then try to embed the tissue at once and as quickly as 

 is possible. Under favorable circumstances this may result in the 

 least amount of hardening, and, if the knife is very sharp, fairly good 

 sections may be obtained. 



If the horny matter is exceedingly refractory it is better not to try to 

 cut it in situ, but to separate it from the surrounding tissues, and cut them 

 separately, the soft parts in the ordinary way, and the horn or nail 

 after some of the macerating and softening methods such as 40 per 

 cent potash solution or strong mineral acids or javelle water. 



LITERATURE 



Several of the papers mentioned after the last part will be useful guides for this. Among 

 those which deal more especially with the poison-secreting tissues are the following : 

 BORDAS, L. "Recherches anat., histologiques, et physiol. sur les glandes venimeuses ou 



glandes des cheliceres des malmignattes (Lalrodecties i3-guttatus Rossi)," Ann. Ac. 



Nat. Zool. (9), Ann. 79, pp. 147-164, i pi., 4 figs., 1905. 

 GUNTHER, A. "On a Poison Organ in a Genus of Batrachoid," Proc. Zool. Soc., Lon., 



1864, p. 157. 

 PARKER, W. N. "On the Poison Organs of Trachinus," Proc. Zool. Soc., Lon., 1888, 



P- 359- 

 WALLACE, LOUISE B. "The Structure and Development of the Axillary Glands of Ba- 



trachus," Journ. Morph., 1893, Vol. VIII, p. 563, pi. 27. 

 REED, H. D. "The Poison Glands of Noturus and Schilbeodes," American Naturalist, 



Vol. XLI, Nr. 489, pp. 553-566, 1907. 



INTEGUMENT, LUBRICATION 



The bodies of most organisms are lubricated with some fluid, and this 

 fluid also acts in other capacities in many cases; as a preservative, a 

 cleanser, a food-gatherer, or even, deserting its original duty, it may be 

 developed as a poisonous substance or a foul-smelling or attractive- 

 smelling material accordingly as it best serves a purpose. Sometimes 

 the fluid is used to lubricate some particular. portion of the body-surface 

 or it may be found on the entire surface. 



The fluid may be produced from all parts of the body-surface or by 

 some parts of it only, which may be further defined from the rest by being 

 invaginated into glands that pour out their secretions on sucn parts 

 of the integument as require it. We may distinguish, according to the 

 kind of fluid that is produced, three principal kinds of lubrication tissues. 



i. A tissue that produces a slimy material called mucin. This sub- 

 stance has a definite chemical basis and is a product that can be used 

 for other internal processes or external processes than those of lubrication, 

 such as preservation of the integument by the retention of water, cleans- 

 ing, the collecting of food particles, the making of cocoons for the eggs, 



