TRANSACTIONS OF THE SECTIONS. 127 



impressed itself on the minds of practical men. Even in the asphyxia or apncea of 

 other accidents, such as drowning-, suH'ocation in coal mines, &c., the artificial 

 stimulus to respiration (electricity), not to the heart, but to the pkrenic nerves 

 has astonished j^^ood observers in German}-, America, Australia, &c. 



Further Observations on Dendroidal Forms assumed hy Minerals. 

 By J. D. Heaton, M.D. 



In this communication attention -was dra-wn to the peculiarities of the den- 

 droidal forms developed upon some purely mineral crystals -when immersed in 

 ■v\-eak solutions of silicate of soda, and some additions were made to the observa- 

 tions upon this subject read at the Meeting of tlie Association at Dundee in 1867. 

 It was then pointed out that when crystals of sulphate of iron, sulphate of copper, 

 or some other mineral salts are immersed in a dilute solution of silicate of soda in 

 the course of a few hours branches shoot perpendicularly upwards in the liquid 

 presenting a remarkable resemblance to the branches of some vegetation. These 

 branches are straighter in a rather stronger solution, more contorted, and some- 

 times distinctly spiral, when the solution is somewhat weaker; but results are 



parallel branches, after gTowing side by side for a time, -will approximate and 

 a^ain anastomose into a single trunk. At the base those developed on sulphate 

 ot iron may have a diameter of one-sixteenth or one-twentieth of an inch ; as they 

 elongate they gradually narrow to that of a fine hair. They have a definite limit 

 of growth, restiicted to a height of from four to six inches." Those developed on 

 sulphate of copper are shorter and more delicate than those on sulphate of iron. 

 When the power of growth fails they terminate in fine needle-shaped extremities! 

 The author had stated at Dundee his opinion that the terminations of branches 

 still in process of elongation presented pointed extremities, which -svere carried 

 forward as growth proceeds, necessarily implying an interstitial mode of increase. 

 But haying since made an arrangement by which branches may be observed mi- 

 croscopically in the act of growth, he must n<^w correct that statement. No change 

 of size or form can be observed in a branch subsequent to its first development ; 

 but as a branch elongates, it narrows as the power of growth fails, and when the' 

 needle-shaped point is formed, there i.s no more elongation. The growing-point of 

 an elongating branch, as seen under the microscope, appears enveloped in a slio-ht 

 cloudiness in the liquid medium, which is gTadually lifted up and precedes the 

 extremity of the elongating branch, whose gradual and continuous development 

 presents a very curious appearance. The branches are delicate tubes, havino- thin 

 semitransparent walls ; they fall in pieces -^v-fien taken out of their native ""fluid. 

 Under a high power of the microscope their walls present a finelv gTanular struc- 

 ture, but no trace of crystalline form. Both the silica of the solution and the con- 

 stituents of the crystal on which the branches grow enter into their formation. 

 What is the nature of the force which determines the assumption of dendroidal 

 forms and a tubular structure by these strictly mineral formations, and their 

 upright growth, in opposition to the tendencies of gravitiition, like the ascendin»- 

 axis of a plant ? It is neither simple aggregation, not is it crystallization. It 

 presents certainly, in its results, a remarkable resemblance to that force by which 

 is eftected the growth of living tissues under the influence of vitality, aiad upon 

 which it may serve to throw some light. And thus these dead structures assu- 

 ming the forms, and increasing so much after the manner, of living tissues seem to 

 eflect one slight gap (amongst others) in that wall of separation by which it has 

 hitherto generally been held that the mineral world is absolutely divided from the 

 world of organization, but which now seems at various points to be o-ivino- ^av 

 In connexion with this subject, the author noticed a communication by Mr W c" 

 Eoberts to the 'Journal of the Chemical Society' upon the occurrence of oroanic 

 forms m colloid silica, as obtained by Graham'sVocess of dialysis. These speci- 

 mens have all the appearance of microscopic fungi, presenting radiating fibres com- 

 posed of elongated cells, with occasional clusters of cells having the appearance of 



