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Rh out any dissection. Most areolar tissue may be distended by forcing air into it, and then innumerable cellular spaces are seen communicating with each other in it; it is not known whether these are produced artificially, or whether they existed previously. Areolar tissue also frequently contains fat-vesicles, which, according to Gurlt, are surrounded by a thin and transparent, but not fibrous, pellicle, often have an hexagonal form, and in that respect resemble vegetable tissue. (Gurlt’s Physiologie der Haussäugethiere, p. 19.) In order to become acquainted with the relation which these constituent parts of areolar tissue bear to the elementary cells, we must refer to the formation of the tissue in the fœtus.

If we examine some areolar tissue from the neck, or from the bottom of the orbit of a fœtal pig measuring three inches and a half in length, we shall find it to be a gelatinous substance, somewhat more consistent than the vitreous humour of the eye, and, in its earliest state, quite as transparent; as development proceeds, however, it becomes more of a whitish colour, and loses its gelatinous quality. When examined with the microscope, small corpuscles of various kinds are seen in greater or less numbers; they are not, however, sufficiently numerous in a fœtus of the size specified to form the entire gelatinous substance, but must necessarily be situated in a transparent, structureless, primordial substance of a gelatinous nature, which we will for the present call cytoblastema. The whiter this substance appears to the unaided eye, the greater is the number of corpuscles contained in it; their quantity, therefore, is continually increasing during development, while that of the cytoblastema constantly diminishes. As in consequence of its transparency, the cytoblastema cannot be seen, but is only inferred to exist from the circumstance that the corpuscles, which are visible under the microscope, could not, at the period when they are but few, form the entire jelly, and that when moved, it is plainly seen that they are held together by some invisible medium, so it is no longer possible to convince ourselves of its existence, when the corpuscles are very numerous. It is probable, however, that it remains between the fibres of the areolar tissue throughout life.