October 2 i. 1897] 



NA TURE 



589 



This occurrence of Foraminifera is of great interest, taking 

 into consideration the age of the beds ; for, so far as I am 

 aware, excepting the occurrence of the remains recorded by 

 Dr. Cayeux from Pre-Cambrian beds in Brittany, and the 

 foraminiferal casts in the Lower Cambrian of tlie Baltic Pro- 

 vinces described by Ehrenberg, these are more ancient than 

 tliose of the well-known discoveries of Brady, Blake, Ulrich, 

 and others, in beds of Ordovician and Silurian ages. So well 

 preserved are these Upper Cambrian Foraminifera that the 

 finely perforate structure can be seen here and there, which 

 leaves no doubt as to their position as members of the Hyaline 

 group of the Foraminifera. Frederick Chapman. 



Acquired Immunity from Insect Stings. 



• In connection with this subject (see Nature, vol Iv. p. 533, 

 0/ alibi), it may be interesting to quote the following passage 

 from "An Account of a Journey to Leetakoo," performed by a 

 Dutchman, named Truter. in 1801 (appended to Sir John Bar- 

 row's " Voyage to Cochin China" (London, i8o5), wherein the 

 passage occurs on p. 382) : "It was remarked that ... the 

 sling of a scorpion, which to Europeans and colonists is always 

 attended with dangerous consequences, . . . has no ill effect on 

 this people [the Bosjesmans], which they endeavoured to explain 

 bv saying that while children being accustomed to be stung by 

 these insects, the poison in time ceases to have any effect on 

 them, as the small-pox-virus loses its action on a person who 

 has had the disease." Kumagusu Minakata. 



October 1 1. 



A NEW CLASS OF ORGANIC ACIDS. 



\ RECENT paper by Prof. Claisen in Liebig'' s Annalen 

 ■^*- (297, 1-98) is interesting, not only because it is one 

 of a series of valuable contributions which he has pub- 

 lished during the last few years, but also because it 

 contains important observations on the occurrence of 

 strongly marked acidic properties in certain hydroxy- 

 methylene derivatives. 



Ever since Lavoisier attributed to oxygen the role of 

 "acidifying principle," attempts have been made to 

 assign a similar function to particular atoms or groups ; 

 and at the present time we say, that a substance pos- 

 sessing the properties of an "acid " contains, in addition 

 to hydrogen or hydroxyl, some so-called acid-forming or 

 electronegative atom or group of atoms. Consequently , 

 when we meet with an organic substance having in any 

 degree the characters of an acid, we immediately associate 

 these properties with the presence of this or that "acidi- 

 fying principle." We account for the readiness with 

 which the phenolic hydrogen atom is displaced by alkalis 

 by saying that the hydroxyl group is influenced by com- 

 bination with the electro-negative or acid-forming phenyl 

 radicle ; and we say that the reason why the alkali j 

 derivatives of phenol are decomposed by carbonic acid, 

 whilst those of the nitrophenols are not so decomposed, { 

 is because in the latter the acid character of the hydroxyl \ 

 group is further enhanced by the presence in the molecule \ 

 of the nitro-group. 



Phenol (carbolic acid) and nitrophenol, however, we do | 

 not usually call "acids," and we cautiously speak of their i 

 metallic "derivatives" and not of their "salts" in order j 

 to avoid the use of terms which might be misleading. , 

 SiiTiilarly we speak of the metallic " derivatives" of nitro- j 

 methane, of ethylic malonate, of ethylic acetoacetate, &c., \ 

 but we do not call the parent substances " acids." 



It appears, however, that the time has now come when 

 we must admit a new class of substances, nainely, the 

 hydroxymethylene derivatives recently prepared by Prof. 

 Claisen, to the distinction of being called "acids." The 

 substances in question may all be referred to the type 



j^(-Q^C = CH.OH, where R represents either an alkyl- 



group (CH3 — , C^H-— , &c.) or an alkyloxy-group (CH3O— , 

 CjH-O— , &c.), and they are described by Prof. Claisen 

 as follows : — They are all strong monobasic acids. They 

 can ail be accurately estimated by titration with normal 



NO 1460, VOL. 56] 



alkali in aqueous alcoholic solution. They dissolve freely, 

 even in the cold, in aqueous solutions of alkali acetates, 

 liberating acetic acid. The determination of the electrical 

 conductivity gave a value for K greater than that obtained 

 for acetic acid. Among substances composed of carbon, 

 hydrogen, and oxygen only, and not containing a car- 

 boxyl-group, they are doubtless the first which approach 

 the monocarboxylic acids (excepting formic acid) in 

 strength, and even surpass some of them. 



The acid character of these compounds may of course 

 be accounted for in the usual way, and, as Prof. Claisen 

 points out, the substances may be regarded as formic 

 acid, O = CH.OH, in which the oxygen atom has been 



R CO 

 displaced by the group r"co^^ '^' ^^^'^^ '"^^^^^ <^°"' 

 tains the two electronegative radicles (R — CO—), ; never- 

 theless the possession of such strongly acidic properties 

 by compounds of this kind is a fact *of extraordinary 

 interest and almost as disturbing to our preconceived 

 ideas as was the discovery of an acid containing only 

 nitrogen and hydrogen. F. STANLEY KiPPING. 



DRAINAGE AND IRRIGATION WORKS 

 IN MEXICO. 



I'^HE valley in which Mexico is situated is almost 

 unrivalled for its beauty, and is encompassed on all 

 sides by great mountain ranges clothed with cedars and 

 pines. The land is extremely fertile, notwithstanding its 

 elevated position of 7000 feet above the level of the sea. 

 Although thus beautifully placed, and at such a great 

 elevation, Mexico was considered one of the most 

 unhealthy cities in the world, the death-rate amounting 

 as high as 40 per thousand ; the cause being the want of 

 proper drainage. The valley forms an immense basin 

 covering 2220 square miles, hemmed in with solid walls 

 of rock, and having only two or three high passes out of 

 it. The valley thus shut in formed at one time an inland 

 sea, but owing to earthquakes and other causes the water 

 gradually subsided until it becaine confined to six great 

 lakes. Each of these lakes is fed by streams from the 

 mountains, which in winter frequently cause the lakes to 

 overflow and inundate the adjoining land. It was in the 

 iTiiddle of this valley that the .Aztecs founded their city of 

 Tenochitlan, building their houses and temples on piles. 

 Subsequently as the water lessened and the fear of in- 

 undation became less, the dwellings were placed on the 

 water-logged ground. 



This was the condition of the country when Cortez 

 chose this site as the capital of New Spain. The old 

 canals were filled up, the city was extended, and great 

 walls built to keep out the water. The city, however, 

 was subject to frequent inundation. In the seventeenth 

 century, after a great flood, the water stood at the level 

 of the second story of the houses for several years. 

 Various attempts were made to obtain an outlet for the 

 water, and in the seventeenth century a canal to miles 

 in length, with a tunnel 10 iniles long through the 

 mountains, was constructed, in which 15,000 Indians were 

 engaged, which partially answered the purpose for which 

 it was intended. The tunnel subsequently becainc 

 blocked after an earthquake by the sides falling in, owing 

 to their having been only supported by tiinber. 



The tunnel having become useless, it was determined 

 by the Spaniards to open it out, but 150 years were 

 allowed to elapse before this was finally accoinplished 

 in J 789. The excavation is 14 miles long, and 

 measures about 300 feet in width and 180 feet in depth. 

 Through this cut, which has assumed the appearance of a 

 natural gorge, the Mexican Central Railway now runs. 

 During the time the work was in hand the locality be- 

 came depopulated, owing to the insatiable demands for 

 labourers, and finally these had to be imported from 



