In [*On Utumi's ring of quotients*, Canad. J. Math. 15(1963), 363-370][1], J. Lambek says:

> As a matter of historical record, the minimal injective extension of a module is a special case of the "algebraic closure" of an algebraic system considered by K. Shoda in his paper [*Zur Théorie der algebraischen Erweiterungen*, Osaka Math. J., 4 (1952), 133-144][2]. 

Since I cannot read German, I cannot understand what the paper by Shoda says, although I think that he does defer the definitions to his previous papers *Uber die allgemeinen algebraischen Systeme I-VIII*.

I would like to know:

1) What exactly his algebraic systems are (maybe the varieties of universal algebra?).

2) Which are his fundamental results about said systems (in these or other papers).

A published translation/review/summary would serve me perfectly. The MathSciNet reviews of the first papers are too vague, enumerating examples and talking about "certain operations", "various relations", etc.

  [1]: https://cms.math.ca/openaccess/cjm/v15/cjm1963v15.0363-0370.pdf
  [2]: https://ir.library.osaka-u.ac.jp/repo/ouka/all/11545/omj04_02_04.pdf