896 



SCIENCE. 



[N. S. Vol. II. No. 52. 



fact that, in the cells of the stamens of Trades- 

 cantia, the hairs of the nettle and of Malva, 

 where streaming movements of the protoplasm 

 are known in the protoplasmic strands tra- 

 versing the interior of the cells fine fibril- 

 like structures are seen to he connected into a 

 mesh or net even in the living cells. Does not 

 the foam hypothesis account for these apparent 

 networks in actively streaming protoplasm bet- 

 ter than any other? The eggs of different 

 animal groups show also a reticulum. In sec- 

 tions of the eggs of the sea urchin, Sphferechi- 

 nus, the well known radiated appearances about 

 the centrosomes are seen connected by trans- 

 verse lines to form a network, or, as it is inter- 

 preted, a radial series of alveoli or vesicles ex- 

 tending in all directions from some central 

 vesicles that form the so-called centrosome. 



The red blood corpuscles of the frog show a 

 reticulum with marked alveolar border. Net- 

 works are seen in the living cells in the bran- 

 chial epithelium of Gammarus and in living epi- 

 thelia of rotifers ; also in the cells of the giz- 

 zard and foot glands of rotifers and in the epi- 

 dermis of the earthworm when preserved. Sec- 

 tions of Branchiobdella show reticular appear- 

 ances in the cells of the peritoneum and epi- 

 dermis as well as in the cuticle itself. In the 

 same way the cuticles of Phascolosoma and of 

 Distomum are found to have a reticular struc- 

 ture like that of living protoplasm. Various 

 tissues in the vertebrates show a reticular char- 

 acter; sections of the liver cells of the frog and 

 rabbit, the epithelium of the small intestine of 

 the rabbit, macerations of the capillaries in the 

 spinal cord of the calf and of connective tissue 

 in nerves of the frog. Pigment cells in the 

 parenchyma of Aulostomum and ganglion cells 

 in the earthworm and in the crayfish again 

 show the same froth-like reticulum. Nerve 

 fibres present special arrangements worthy of 

 consideration ; in the teased nerve of the frog 

 there are longitudinal fibrils 6-7 microns apart 

 connected by transverse meshes ; similar ap- 

 pearances of elongated meshes in rows are seen 

 in the nerves of the crayfish, rabbit and calf 



In all these cases what is actually seen is but 

 a network appearance and not a foam structure, 

 yet as the artificial mass that seems undoubtedly 

 to have a foam structure presents under the 



microscope the same network appearance as 

 that seen in the protoplasm, there is a strong 

 inference that this also is due to an actual foam. 

 The resemblance between the appearances of 

 the artificial foam and protoplasm is well seen 

 in the so-called ' false networks ' common to 

 both. When fine granules of India ink are seen 

 in water, or when fine oil drops are shaken in 

 soda and compressed, there is formed a network 

 of triangular meshes by the combination of 

 diffraction rings about the separate spherules. 

 Prof. Biitschli claims that the same ' false net- 

 work ' is seen in sections of liver and in other 

 protoplasmic structures in addition to and on a 

 higher level than the true network caused by 

 the alveoli. 



The foam theory assumes that protoplasm is 

 in the fluid or viscid fluid state, but this re- 

 quires demonstration, since many have held 

 since the time of Briicke that protoplasm con- 

 tains solid elements as part of its structure. The 

 network is often regarded as a solid portion of 

 the mass. The following considerations, how- 

 ever, tend to establish the fluid nature of pro- 

 toplasm. 



The vacuoles in protozoa are spherical and 

 must hence be surrounded by fluid protoplasm. 

 The flowing together of such vacuoles and their 

 membrane-like envelopes are readily intelli- 

 gible on the foam theory, but not if we assume 

 that the network is a firm structure. The idea 

 of a firm network involves that of a porous sur- 

 face and the reformation of a new surface with 

 solid supports when the mass is burst ; on the 

 foam theory the alveolar layer of closed ves- 

 icles makes the boundary of all surfaces and the 

 laws of fluids reform this surface, however 

 often the mass may be ruptured. The alveolar 

 layer has no explanation on any but the fluid 

 foam theory. This remarkable layer of cham- 

 bers or vesicles is not a membrane, but a fluid 

 layer, as may be seen in the cell division and 

 conjugation of infusoria; yet it may in some 

 cases be so modified as to become a membraue, 

 or even a cuticle or chitinous shell, as in Arcella. 

 The assumption of a fluid foam structure ex- 

 plains the radiated arrangement which the 

 meshes of the network present around the 

 nucleus and vacuoles. The fluid nature of pro- 

 toplasm is also supported by the iact that gran- 



