Aug. 1st, iSS;.] 



SCIENTIFIC NEWS. 



129 



and winter, and is most abundant in wet weather, when 

 it is least needed, and it must be purified. The farmer 

 wants it only at certain times of the year, in certain kinds 

 of weather, and for certain crops. Hence it is necessary 

 that the sewage should be distributed, or be at least capable 

 of distribution over a very large area, so that some portion 

 of the land may be always in a condition to receive the 

 stream. Ordinary prudence would stipulate that the 

 sewage should be turned off from any field or market gar- 

 den for a fortnight before the herbage is cut for the use of 

 cattle, or before vegetablesand fruits — especially those which 

 are commonly eaten raw, such as lettuce, celery, strawberries 

 — in order that full time may be given for any faecal matter to 

 be assimilated by the plants. Night-soil has long been used 

 without unpleasant consequences for manuring fields and 

 gardens ; but it was generally applied in the late autumn 

 or winter, and was not brought into close proximity to 

 vegetables immediately before they were gathered. It will 

 be remembered that during the last visitation of cholera at 

 Paris, the inhabitants were warned by the sanitary authority 

 against consuming the produce of the celebrated irrigation 

 fields of Gennevilliers. 



In our next issue we shall consider the drawbacks to be 

 combated in the treatment of sewage by precipitation. 

 (To be continued.) 



The RED COLOURING MATTER of BLOOD. 



ALL the animals most familiar to us, such as quadrupeds, 

 birds, and fishes, contain red blood. Quadrupeds and 

 birds are so charged with this red fluid that it pours out 

 copiously when they are wounded, and their flesh is red, i.e., 

 deeply stained with the colouring matter of blood. The 

 greatest quantity of blood found in any animals of their size 

 is met with in seals and other diving quadrupeds, which are 

 very troublesome to the dissector on this account. If the 

 body of a fish is opened, a very different state of things is 

 found. The blood is scanty, and only flows freely from a 

 few large vessels, while the muscles, as a rule, are pale or 

 white. A fish, we may remark, is usually poorly nourished 

 in comparison with a quadruped, and rarely contains any 

 fat. We see, then, that in quadrupeds, which are ordinarily 

 active and well-fed, as well as highly organised, much red 

 blood is found ; and that this is especially the case with those 

 quadrupeds whose mode of life is liable to interfere with 

 free and regular respiration. On the other hand, fishes, 

 which are the lowest and worst-provided of vertebrate 

 animals, contain little blood. A few fishes, however, e.^. , 

 the salmon and sturgeon, which have exceptional oppor- 

 tunities of growing fat, get a tinge of red in their muscles — 

 an indication of the comparative abundance of their blood. 



Why is blood red ? We can only answer the question 

 partially by saying that blood contains a red substance upon 

 which its usefulness almost entirely depends. Blood has 

 two functions— nutrition and respiration ; and these are 

 closely connected, as is shown by the fact that venous blood, 

 which has given up its oxygen, has absolutely no nutrient 

 value. The respiratory office of the blood is discharged by 

 a red substance (heemoglobin), which is contained in a state 

 of solution by the red corpuscles. Haemoglobin is a crystal- 

 line body, the crystals being easily procured from the blood of 

 some animals (horse, cat, dog, rat, etc.), but with difficulty 

 from others (man, ox, sheep, rabbit, etc.). The physio- 

 logical use of hsemoglobin turns upon the singular facility 

 with which it absorbs oxygen, and the equal facility with 

 which it gives it up to any tissues poorer in oxygen 

 than itself. Haemoglobin is like a sponge, absorbing 

 greedily, but parting at the slightest squeeze with what it 

 has absorbed. It is possible to separate haemoglobin into a 



proteid constituent and a brownish-red substance, which 

 sometimes shows a metallic lustre (haematin). An alkaline 

 solution of hcCmatin is prone to take up oxygen and to part 

 with it again ; so that it is probably in the hasmatin that the 

 oxygen-carrying power of haemoglobin or of red blood 

 resides. Hasmatin contains the elements usual in animal 

 compounds, viz., carbon, hydrogen, oxygen, and nitrogen, but 

 to these is added a trace of iron. Inconsiderable though the 

 iron is in quantity, it is of essential importance; for if it be 

 removed by acids, the haematin at once loses its oxygen- 

 carrying power. 



Though haemoglobin is very general in vertebrates, it is 

 not quite universally present in them. The little fish, am- 

 phioxus, and not a few of the pelagic fish-larvae known as 

 leptocephali, are destitute of haemoglobin, and consequently 

 of red blood. All these are transparent fishes, distinguished 

 by the almost gelatinous texture of their tissues and the 

 delicacy of their skin. 



Invertebrate animals, such as snails, worms, and the like, 

 seldom contain red blood. They often, it is true, contain a 

 fluid which circulates like blood, and has something of the 

 same microscopic appearance ; but invertebrate blood, as a 

 rule, is either colourless or tinged with some other colour 

 than red. Now and then, however, even invertebrate 

 animals are found to possess true red blood, containing 

 haemoglobin. Most of the examples are met with among 

 the worms. The common earthworm, the leech, the little 

 red worm (tubifex) found in muddy pools, the lobworm 

 found on sandy shores, and the nemertine worms, which 

 wind in and out of the mud and stones in shallow seas, are 

 among the most familiar. It is noticeable that a great pro- 

 portion are burrowing animals, and this is pretty commonly 

 the case with other invertebrates which contain red blood. 

 MoUusks are nearly always destitute of haemoglobin, but the 

 burrowing razor fish (Solen legumen) is an exception. In- 

 sects, too, follow the same rule ; indeed there is but a single 

 exception among them. The " blood-worm," or the burrow- 

 ing and aquatic larva of a dipterous fly (chironomus), con- 

 tains haemoglobin in its blood, which altogether disappears 

 when the insect begins to breathe air. The common house- 

 fly contains a red substance in its body, but this is not 

 haemoglobin, as the spectroscope shows. Lastly, there are 

 two or three freshwater Crustacea which possess haemoglo- 

 bin. It is significant that so large a proportion of the red- 

 blooded invertebrates should be burrowing animals, and we 

 can readily see that they require an oxygen-carrier all the 

 more because they can aerate their blood only at a small 

 part of the surface of the body. The same principle seems 

 to govern the distribution of haemoglobin in vertebrates, 

 though here the proportions of the species with and without 

 haemoglobin are reversed. Vertebrates are very generally 

 thick-skinned animals, of large size, breathing by definite 

 respiratory organs, and consuming much oxygen in conse- 

 quence of their activity and rapid metabolism. The very 

 few which have not red blood are of small size and low 

 grade, and have a skin so thin and absorbent as to allow 

 the exchange of gases through it. 



Tolerably complete lists of the animals with and without 

 haemoglobin seem to point almost inevitably to some such 

 explanation as we have attempted to give, but we are far 

 from claiming that the subject is cleared up. For instance, 

 we have pointed out that a large proportion of the inverte- 

 brates with haemoglobin are burrowing animals, but if any- 

 one should ask why do not all invertebrates which burrow 

 possess haemoglobin, we must admit that the question is too 

 hard for us. Failure to answer it does not, however, 

 necessarily overthrow the explanation. We may affirm that 

 the reason why some people wear wigs is that they have 

 lost their natural hair, and this account of the matter would 



