of the Fishery Board for Scotland. 



21 



third day — that is after 60 hours- -the blood presents the appearance of 

 an amber-coloured field. The corpuscles have nearly all broken down 

 and their contents have escaped. In each field there will now be seen 

 many micro-organisms, some of which are motile, and a few fragmentary 

 corpuscles. The blood for examination was always taken from the 

 cardinal vein in the caudal region, but on the third day the fluid in this 

 vessel was very scanty. 



The discoloration of the tissues, which produces the appearance of a 

 reddish-brown ventral line, will be observed to commence circumjacent to 

 the caudal vein, and inferior to the vertebral column. It then spreads 

 outwards and round the vertebral column, staining the adjacent muscle, 

 until there is a column of tissue from |-inch to J-inch in diameter dis- 

 coloured. If the muscular tissue round the vein be examined from day 

 to day the commencement and progress of the staining of the muscle 

 fibres is readily seen, and by the third day (60 -72 hours) micro-organisms 

 are readily detected amongst the tissues, although none will be found 

 in the tissues immediately after death, when examined with proper 

 precautions. 



These examinations were made by both wet, dried, and stained micro- 

 scopic preparations, and by ordinary culture media. An account of the 

 extended bacteriological examination of the nature and properties of these 

 micro-organisms will be given elsewhere. 



From these investigations it appears that the micro-organisms present 

 in the blood before death, as also those that gain entrance after death, 

 multiply rapidly in the blood, which forms a suitable nutrient medium, 

 while at the same time the red blood cells disintegrate, and their colour- 

 ing matter or haemoglobin is set free. Both micro-organisms and 

 colouring matter soon make their way through the wall of the blcod 

 vessel. The former can be detected among the tissues, while the latter 

 causes the reddish- brown staining of the tissues and forms the red 

 streak along the ventral aspect of the backbone. It will be noticed that 

 this staining does not increase beyond certain limits as putrefaction 

 proceeds, the reason being that the blood is limited in quantity, and 

 therefore in its staining powers. These changes occurred in all the fish 

 examined, such as haddocks, whitings, cod, herring, plaice, etc., and they 

 occur in gutted and ungutted fish alike. 



The chief value of observing the presence, degree of development, or 

 absence of this sub-vertebral red streak is that it indicates fairly accu- 

 rately the length of time since the fish were captured or landed. 

 Recently in some fishing districts it has been attempted to remove the 

 sub-vertebral blood vessel along with the gut at the time of capture. In 

 the fish trade, haddocks with well-marked red discoloration will not 

 readily sell as fresh fish, and are usually cured. When cured, the red 

 discoloration is still present, and such a fish will be slightly sour to taste 

 and smell, and its keeping properties are impaired. 



10. Rigor Mortis. 



The study of rigor mortis in fish is a subject of no less importance to 

 those engaged in the inspection of fish in the interests of public health 

 than to trawl fishermen and fishcurers, who are so often concerned in 

 the preservation of fish as long as possible in the fresh state. 



Physiology teaches, and it is a matter of simple experiment, that 

 muscular tissue retains its property of irritability, and will therefore 

 respond to stimuli for some time after the death or destruction of the 

 brain and the cessation of all voluntary movements. The stimuli may be 



