THE VICTOUIAN NATCJIt ALIST, 13 



I trust the mode of preparation has now been made sufficiently 

 clear, so that anj' one may follow it out with success, and avoid the 

 Toitfalls and disappointments of my own early attempts. 



These dry preparations hnve their advantnges and their drawbacks. 

 One drawback is the loss of their natural colour, but fortunatelj^j, 

 this can be remedied to a certain extent if desired. By painting 

 with oil-colours, the specimens may have their living tints restored. 

 On the other hand, they combine the advantages of a spirit— 

 preparation or a model, without their disadvantages. When properly 

 prejiared, the parts are of leathery consistency, and overlapping- 

 parts can be turned aside to show those lying beneath, and just as 

 in a model, certain parts may be specially coloured to bring them 

 into prominence, so here the same may be done. There is another 

 great advantage which would not strike the ordinary observer, and 

 which gives an additional value to these preparations. By the very 

 mode of prepai-ation, not only the external form, but the microscor>ic 

 structure is preserved. And this suggests a remark. I was struck 

 with the fact that this very method was employed by Mr. Lockhart 

 Clarke, in making his beautiful microscopic preparations of the 

 spinal cord, some thirty years ago. 



According to his method, a portion of perfectly fresh spinal cord 

 is hardened by steeping in dilute chromic acid solution, soaked in 

 spirits of wine to remove the water, and then treated with oil of 

 turpentine. So that a jirocess then used for microscoiiic preparations, 

 is now used for macroscopic preparations, and it occurred to me that 

 here was a hint which might be turned to good and useful account — 

 the application of microscopic methods to larger objects. 



A very good further illustration of this principle has just come 

 under my notice within the last few days, and if it had been 

 recognised, what is now reported as a remarkable scientific discovery^ 

 might have been anticipated long ere this. 



Microscopists are familiar with the fact, that if it is wished to 

 observe the changes undergone by the blood in its active condition, 

 it is necessary to have the preparation enclosed in oil, and they as 

 well as biologists, are likewise familiar with the fact, that the 

 coagulation of the blood soon after its effusion, has been a great 

 hindrance to experiments with micro-organisms, since all the means 

 hitherto tried to prevent coagulation have been more or less 

 unsatisfactory, because they altered the chemical composition of 

 the blood. 



A student, (mark you), in the chemical laboratory of Professor 

 Strieker, at Vienna, has discovered that coagulation can be preveatetl 

 simply by making an oil preparation of it on a large scale. The 

 blood is poured into a clean glass or other vessel, the sides of wldcli 

 have been coated with a thin film of oil, then a layer of oil is poured 

 on the top of it, and the blood is thus preserved fresh for any 



