TMe VICTORIAN NATtfRALlST. lOo 



cent. It is sold in this way for disinfecting purposes, and is not 

 strong enough for general purposes of preserving tissues.) Formalin 

 is colourless and neutral, and has a penetrating and pungent 

 odour. The fumes are said to be not harmful unless inhaled 

 for some hours. It is important to remember that it is very 

 volatile, and must be kept in tightly-closed vessels, or the strength 

 will diminish. I have estimated the specific gravity to be 1.078. 

 It is free from corrosive properties, and is not poisonous or 

 combustible. It is a most powerful antiseptic agent. I have 

 seen it noted that Drs. Stahl, Berlioz, and Trillat proved that in 

 a dilution of i to 50,000 it killed anthrax bacilli. It is, there- 

 fore, as powerful in this respect as corrosive sublimate. But, 

 enough on this head. 



Now, as to its use in preserving animals and plants. For 

 general purposes I consider the best strength is between 

 5 and lo per cent., certainly no stronger. I have many suc- 

 cessful examples in which I have used only 2 per cent, strength, 

 but I have also had a few failures with it. I think 5 per cent, 

 will be found strong enough for nearly all substances, provided it 

 is changed to a fresh supply after the first day or two of treating a 

 specimen ; and in larger specimens it should be changed every 

 day for a longer or shorter time, according to the size of the 

 specimen, or, failing this, a drop or two of formalin should be 

 added occasionally, according to what the tissue is, to make up 

 the loss of strength occasioned by mixture with the water of 

 organization. 



You will notice from my specimens that it preserves animal 

 structure without causing any perceptible shrinkage, nor does it 

 coagulate the albumen, as alcohol does, by extracting the water 

 from the tissues. The colour of the blood in tissues changes to a 

 brownish shade, but may be restored at any time by immersion 

 in strong alcohol. Methylated spirit answers ; and I will give 

 you a few practical examples, when you will notice the colour 

 reappear as fresh as ever, and the blood-vessels become defined 

 with the greatest fidelity. Dr. Blum, I think, was the first to 

 publish this. 



With formalin the chlorophyll in plants is not dissolved out as 

 with alcohol, and the colour of flowers is more or less preserved ; 

 but I have not experimented to any extent in this department. I 

 exhibit five examples to-night. 



I have noticed, as others have frequently done, that the 

 microscopical structure of the tissues is faithfully maintained, the 

 cell contents are well preserved, and the nuclei in those from 

 5 per cent, solutions or stronger remain distinct; also they allow 

 of staining with carinine and aniline dyes. 



Formalin mixes readily with many chemical compounds, and for 

 special work I have experimented with it in varied combinations. 



