ORIGIN AND NATURE OF THE MUCILAGE IN THE CACTI 163 
much more viscous product. Carnegiea yields a mucilage of low viscosity, 
quite as low as that of Tilia. Indeed I find like differences between dif- 
ferent species of Opuntia. Doubtless a refined technic would discover 
chemical differences between these various mucilages. Here it is only to 
say that the distinction between a "gum" and a mucilage is not, at the 
present, one which corresponds with the manner of origin of these substances. 
It is pertinent in this connection to remark that Tschirch's organological 
classification is in a sense inadequate, as it brings into association mucilages of 
distinctly different kinds: e.g., salepis intercalated between the mallows and 
tragacanth. 
Chemical and Staining Reactions of the Mucilage 
The determination of the chemical composition of the mucilage is ob- 
viously a problem within the field of biochemistry, and it is, therefore, not 
my purpose to pass beyond the limits set by the methods I have used. 
It has been shown that previous to the occurrence of mucilage, the 
inner zone of the cell wall gives the reaction of hydrocellulose. The mucilage 
itself gives no indication of this origin, as with iodine and sulphuric acid it 
colors only yellow or brownish. It is therefore a cellulose-mucilage if 
regarded from the point of view of its origm. 
It is hydrolyzable by chromic acid, though very considerably more 
resistant to this reagent than the middle lamella. The tissues may be 
immersed for several hours in io% chromic acid, whereby the mucilage 
cells are set free in their entirety, and, after washing, may be preserved 
indefinitely in water, and in this condition afford practically unaltered 
pictures. If the action of the reagent is more prolonged, more or less 
swelling occurs and consequent rupture beyond the confines of the cell 
walls. Ultimate complete hydrolysis follows still longer treatment, espe- 
cially at higher temperatures. 
The mucilage is hydrolyzed also by sulphuric, nitric, and hydrochloric 
acids. 
It submits slowly to the digestive action of organisms. The time occu- 
pied in materially reducing the viscosity of a solution sufficiently for it to be 
recognizable to the eye was about six weeks. At the end of eight to ten 
weeks the viscosity had been lowered to that of water, or nearly so. A 
second lot, having an initial viscosity several times greater than the above, 
still shows after six months a considerable viscosity, but much nearer to 
that of water than to its initial viscosity. During the process a series of 
odors has been produced, some of which were undoubtedly due to protein 
putrefaction. The organisms involved are not yet determined. 
Staining 
No attempt has been made to exhaust the possibilities of staining the 
mucilage cells in the ordinary sense. For the purpose of demonstrating 
^° For the ordinary methods see Strasbiirger-Koernicke's Botanisches Practicum; 
Tunmann; Tschirch. 
